I’m almost certain this is not possible. Allowing hotlinking is an all-or-none proposition as far as .htaccess is concerned. At the moment I can’t think of any workaround that might do what you want.
I’m not positive but I believe you can place the .htaccess in a subdirectoy(not sure that’s the right term). Anyway, it will only block what is placed within that, so you could place the icons you don’t want linked to there and the others elsewhere. You would of course have to change the links.
Thanks for the suggestions, but the different folder idea won’t work. I have a user-contributed photo gallery on my Web site, and the vBulletin-based back end dumps all the images into a series of directories that can’t be sorted by size.
This issue then seems to be solely bandwidth limits or cost, not the unauthorized use. AFAIK, placing the htaccess will not stop folks from saving the image, just hotlinking, so perhaps that’s accepatable.
Depending on how you’re setup and how much time you have, you can get software that will “crunch” the file size of the icons so bw can be reduced even if they link.