I have mares vs stallions for my waterhorses, then the minor breeds each just have one. although i have a few others for 'special' horses if I DNA breed or something and want to keep track. Supers all get a personalized picture too. I usually change my main horse pics every year at least to keep myself interested. Havent had time yet this year though. I really have to do at least my peggies soon - i would like to get them mare/stud pics
I think that's everyone? Its easier to just post the links instead of trying to explain how it works xD They in general follow their pics, fillies get the dam pic (unless crossed), colts get the sire pic (same deal). If they are a promising foal from a super they tend to get the parents pic if they have a unique pic, or the grey/brown horses if they don't (or I just don't feel like it). Some horses break the streak either A - because I'm lazy, or B - because I mixed up something, but in general I can just scroll through my horses and know where they come from and where I gotta look out for related lines, whats fresh, whats old, who is most likely to have more DNA, yadda yadda :)
Oh! I also have different pictures for my Firehorses. Firehorses are only second gen, but I will have it so pure foundation lines get pic X & Y for mares and stallys, crossbreds get another pic, and I want to get a few different ones here soon.
Unicorns have/will have custom lineart pics cause I don't have many and its fun.
Pegasi have pictures according to where they came from (DNA bred, Purchased from Person A, B, C, etcetera).