I fear that my eyes are broken. For some reason, no matter how hard I try I can’t see those 3-D images they put in the newspaper. How come? 
I’m assuming you mean those “stereogram” things. You don’t wear contact lenses, by chance, do you? I found that, when I wore contacts, I couldn’t see them either, but I could when I wore my glasses. Probably a combination of funky focusing and not being able to keep my eyes open for long without 'em feeling dry. Haven’t tried any since the laser surgery.
Seeing those things is kind of a knack. Usually they’ll print two dots or squares right below the stereogram. Those can help you; focus on a point beyond the newspaper (look through it, in other words). You should see four dots/squares below the image, two each in the right and left eye. Adjust your focus until the centermost dots/squares merge, such that you see a total of three dots. Hold that focus, and you should see the image. I find that if I look directly at the image, though, I sometimes lose it. Be patient, and you’ll get it.
It’s not well-publicized but those “Magic Eye” drawings are a diagnostic tool for brain tumors. My condolences. 
Seriously, I think it’s just one of those things. My 96-year old grandmother can pick one up and pick out the image right away. It usually takes me about 5-10 minutes for most of them.
2planka,
I’m assuming you’re talking about Magic-Eye or hollusions? It’s all about focus. It’s very tricky to make your eyes focus wrongly the first few times. It gets easier with practice. Here’s a trick that I find usually works for many people I know who used to never be able to see these things (in fact, I often use it to make the image snap into place more quickly).
First move the image very close to your eyes. So close that it is impossible to focus. Concentrate on NOT focusing on the details of the pattern. Now very quickly and smoothly move the image away to about arms length or more. Try to keep your eyes defocused. Move the image very slightly around. Again don’t look at the pattern, but see if you can detect distortions.
Sometimes it helps if you know what you’re looking for. Not so much the object, but rather the effect. Imagine that you have a special spray paint. Whatever you spray takes on the pattern of your hollusion. First you paint the background. Then you paint whatever is in the foreground (i.e. the object you’re looking for). That’s sort of what you’ll see when the image does come into focus.
Hope that helps…
If that’s not what you’re talking about, then sorry for wasting your bandwidth…
If you mean the stereograms that you have to defocus to look at, it’s because there’s a knack to doing it. They usually tell you to focus beyond the image. That doesn’t help me. I find that I can see them if I look at them crosseyed, and then relax the two images to a certain point. Only trouble is that if I do it for too long it gives me a headache.
… anyways. I’ve tried all the stuff you guys mentioned but it still doesn’t work. I can spend upwards of 15 minutes with the damn things and still not see the stupid picture.
I’m astigmatic, with a vertical distortion. Without glasses I have slight over/under double vision. That’s probably the reason why I can’t see 'em. I’ve tried with and without my specs to no avail.
Am I missing anything? Are the images any good or are they dumb?
Well, I have one bad eye (accident when I was 16), and I can’t see those either, nor can I use 3-D glasses. They don’t do anything for me … this is not to mention my f-ed up depth perception.
Eh. Depends on your point of view, I guess. They kinda look like (if you can imagine this) a funky dot pattern with a cutout shape filled in with the same dot pattern hovering above the background. It won’t change your life, but it’s kinda neat.
If one eye is stronger then the other and you know which one it is, you can squint tha eye a bit. This should let your brain acknoledge the week eye’s immage
If you have a spare picture frame or any piece of glass lying around, you can try this trick that has worked for many of my friends.
Put the picture behind the piece of glass and look at your barely visible reflection in the glass. You don’t want a bright light to be reflected, and you do need to stare at yourself for a little bit before it starts to work, but the technique has an almost perfect record around here.
Keep staring.
-or-
IIRC (not sure about this), some small percentage of people just can’t see it due to their physiology.
quick google search
This guy seems to have an answer…
http://www.eyetricks.com/stereograms/stereowhy.htm
You may have a condition called ambliopia. This happens when there is a difference in the visual acuity of your eyes and this goes uncorrected during childhood. If I remember the pamphlet from the ophthalmologists office correctly, the critical age range for the institution of eyesight correction is 2-10yo. If the disparity in visual acuity is not resolved by then, a lifelong condition called ambliopia results, where despite subsequent correction, vision in the eye that was originally of lower acuity will never be normal. My understanding is that this has a neural basis to it. That the brain prefers the higher quality data arising from the better eye, and therefore develops in a way that more effectively uses the visual information from this eye. And sort of dumps the info coming from the bad eye.
What does this have to do with stereograms? It’s impossible to see the stereo effect without binocular (both eyes) vision. I dunno if this is your problem, but it’s a thought.
Another thought: If stereo images you refer to are the colored type. Where you basically see nothing until you stare for a while and then a 3d image magically appears. I’ve noticed that these images are commonly rendered in red and green. I’m pretty sure that the 3d info in them is color encoded. Well, red-green colorblindness is a VERY common condition (something like 5% of males), and IMO would preclude your ability to see the effect in these images.
2planka, I feel your pain. I, also, cannot for the life of me see these images. Don’t feel too badly, 'cause I’m pretty sure they’re a hoax, invented by people without astigmatism and weak eyes 
Okay,
No congenital eye defects here - my siblings can all see the darn things.
First vision difficulty was when I was 17. Tried to catch a baseball with my eye. Not a very good eyedea.
Astigmatism developed after the injury, but I can still read, hit a fastball, shoot trap, and do just about everything else without glasses. My prescription isn’t very strong.
I can see 3-D movies with the silly paper glasses.
I’m not color blind.
Sometimes when I look at a stereogram for a while I have difficulty refocusing when I look away. This can last some time and usually gives me a headache.
If I felt I was really missing something I’d try again, but thanks to you folks I guess life is still worth living even though I’m stereogrammatically challenged. 
Actually, the advice to “focus beyond the page” is incorrect. If the page is 10 inches away, you should focus 10 inches away. That’s why it doesn’t work for you; it doesn’t work for anyone. What you’re doing is what you’re supposed to do: look cross-eyed at it.
Aw, don’t give up! When these first came out a few years ago, I took some to my sister; she couldn’t see them right away and flatly maintained she would never see them. Then her Sunday paper started carrying them and she decided to give it another try. Shortly thereafter I got a call from her, “I saw it! I saw it!”
You can try Magic Eye’s site. And if you still can’t see them, at least the site will show you what the image is supposed to look like!
“Focus beyond the page” is not exactly correct but a good description - let me try to explain. Try holding out a finger in front of your face, say 10 inches away. Then look not at the finger but at the wall beyond the finger. Then try to notice (but not look at) what the finger looks like. You should see a double image of the finger, since your eyes are not pointed at it. Now, hold out two fingers. You should see a double image of two fingers, or four fingers. But if you adjust the distance just right, the two middle fingers should merge, making only three fingers visible.
Now take a piece of paper and draw two dots about an inch apart near the top, and do the same thing. This time, once the two middle dots merge, look directly at the middle dot. It should look like a simple dot, but located farther away than the piece of paper. Using two dots 10 inches away from you, you have fooled your eye into believing there is a single dot 30 inches away. If you vary the distance of the two dots, you can adjust the apparent distance to the dot. You can extend this idea by having hundreds of dots to form imaginary dots at various distances. That’s how random dot stereograms work.
Another method is just to hold the stereogram close to your face, about 5 inches away, and relax your eyes. Pretend you are daydreaming and let your eyes relax and lose focus. Once you get it it becomes easier.
Actually there are two types of “focus” for our eyes. Each eye adjusts its focus to form a sharp image. And each eye must point to the same object. For stereograms, each eye shoud focus to the distance of the stereogram, but the eyes must point to a spot farther away than the stereogram.
When I first saw one of these in around 1992, I didn’t even know what it was supposed to do. My friend had me hold the poster and told me to stare at it until I saw something. I didn’t even know I was looking for 3D. I stared for probably 15-20 minutes, then all of a sudden…POP…the thing came out (well, went IN) and stared me in the face. it was great! I used to have an awesome one of a shipwreck in my bedroom, and I got so good at looking at them that I can usually get them to converge for me within about 15 seconds now. If I know the image, I can do it almost instantaneously.
Jman
One more place to look, if you want a full explanation of how Stereograms work (beyond the website cited earlier), is Steven Pinker’s How the Mind Works. He has an entire section devoted to how the brain interprets magic eye pictures. And there is a physiological condition, beyond poor vision, that prevents some people from being able to see the 3d images.
Word of warning, though: you pretty much have to have read the earlier sections of the book (at least the parts where he discusses vision) to understand the section on magic eye diagrams.
Are you by any chance a strabismic?
Translation: were you born with a “lazy eye”?
To see those “magic eye” pix usually requires binocular vision (both eyes working in tandem). Strabismics typically don’t have binocular vision (unless they were lucky enough to have corrective surgery to realign the “lazy” eye early enough - which I wasn’t), which makes for horrid depth perception and reduction in 3D vision.
I personally have never seen the neato-keen images. Or been able to truly appreciate IMAX or 3D movies. Then again, being a diplopic strabismic (I actually see double constantly) makes life interesting!