PGP will create a self-decrypting archive file which should serve your purpose. Note that this is part of their disk tools set which is not included in every version of PGP (some only include the email tools).
There are a lot of other encryption products which would do what you want. Be aware that many are snake oil (bad encryption hiding behind meaningless marketing verbage). Look for products that use accepted standard encryption algorithms such as AES or Blowfish for symmetric crypto. Shy away from anything that uses a secret algorithm or claims to be “totally secure” or “based on innovative new encryption inventions” since those are words most real security people wouldn’t use.
Another approach you could try would be to brand the images with a huge big ugly watermark so that one can still see and evaluate the image but couldn’t use it for any commercial purposes. If the company then later wants to buy an unwatermarked version of the image they would have to contact you.