Pardon me if this topic has been covered. I didn't find it in searching.
When using photos of models for illustrations, an artist really needs multiple pictures of the same person, from many angles, with many facial expressions. Costumes should be simple, allowing the artist to adapt the model to various scenes and occasions.
Because high-resolution photography allows an artist to "zoom in" for close-ups, photos are more valuable when they show the entire person, allowing the artist to crop the image for specific purposes. If the photographer has shot a picture showing a man or woman from above the knees when the artist requires a full-height image, the photo is almost useless. I have found many images that would have been perfect if only the hands or feet weren't missing.
And each model should have some form of identification that can be used to search for ALL photos of the same person without the tedious task of scrolling page after page looking for a specific expression or angle that may or may not exist.
I hope these suggestions are helpful to all concerned.