1. Some people that pay by the minute for internet access (almost always outside the U.S.) download everything at once and then read offline. Binaries posted to a non binaries newsgroup forces them to pay to download it whether they want to open it or not.
2. If one person posts a pic, then *everyone* thinks they have the right to do so. There is no photo that is so special that it supercedes the basic rule of usenet about binaries in non binary groups.
3. As more people think "well if so and so can post a pic then I can too" the server will expire posts that much faster. If it really gets going, sysadmins will not want to carry the group altogether.
4. It makes Russell Prater's computer crash, and frankly his ability to read and post to this NG is far more valuable than *anyone*'s photos.
5. There is a binary newsgroup set up for this purpose. Something like alt.binaries.pets or something like that (I have no idea, I dont read it.)
What you can do is set up an account with one of the many free web space provides and post your pictures there. Most of us love to look at pictures of ferrets and will gladly follow the link you provide!