Originally posted by Lowell Goudge In my opinion, you probably have no rights at all to the photo any more.
Having sent it out to someone with no copywrite or disclaimer, your image is probably now public domain free for anyone to use.
What I think you should do is ask the person you initially sent it to, if he gave the images, not just yours but all of them to the store for use, and that since they were taken by local photographers, he might suggest the store consider giving the photographers credit for their work.
After that, let it drop, and take the experience forward as to what you do for protection of your images.
If it were a patent issue, you would be correct. This is different. There should be a procedure on campus for grievances , ethics, academic honesty etc. Does your campus have and ombudsman and or provost? Maybe you should contact the faculty senate office about where to start.
Edit: One other thing: In some states, official business conducted via email can be requested as long as it doesn't have student or personal info in it. Private schools would be different. Regardless, your email to the person you sent it to is a piece of evidence.
Also, did you ask here who this professional photographer was that she hired?
Finally, is there anything unique that is in your photo that would make it unlikely to duplicate such a a combination of people at a scene at the Student Union?