I work at a ranch and we are constantly asking people not to photograph the horses. I have been to other ranches that have signs asking the same. I think this is fair because owners Spend a lot of money on having photos made to make their horses look their best. Someone comes along with their cell phone in bad lighting and posts it and it is not flattering to say the least 

any suggestions what a sign should say without being offensive? 

what's your pet peeve? 

I have mixed feelings about this. I understand that the owners want the pictures out there that make the horse look their best, but some times the "best" is far removed from reality. It's a pet peeve of mine to go look at a horse/stud that looks NOTHING like the advertising picture. To the point that I will not breed to a stud I haven't 1) preferably seen in person, 2) gotten candid pictures from ALL angles including legs or 3) on a video. I guess it's reasonable to ask somebody that is there to not take pictures, because they are there physically seeing the horse, and I do understand that people can take crappy pictures, but sometimes those "bad" pictures are a lot more truthful than the "good" ones.  

Any Pictures Are For Personal Use Only--NONE To Be Shared On Social Media Unless Approved.