The higher the resolution of your reference picture, the better the painting comes out. It’s easier for me to see small details that make the pet unique. Also, the less saturation/filters (I’m looking at you Instagram pictures!) the better. 

When your pet is in natural lighting, it’s easier for me to pick the right colors to represent their coat. Pictures with bright sunlight or shadows can be difficult to capture in a painting that is focused on the pet itself. 

Giving me multiple pictures to reference is also very helpful. If I can’t see something in one picture (like eye color), I can at least reference another to help decipher any unique qualities of the pet.