This is from the Reference Image Library FAQ's which is in a pinned post at the top of this forum.
The people who put their photos in the RIL still own the copyright to their photos but understand that by putting them in the RIL the photos are being used as references. I would contact the person(s) who's photos you used to let them know if it's worrying you though.
Do I need to ask permission before creating art from a photo in the library?
The person who uploaded the image granted that they own the copyright to the image and that the general public may use it to create new art. It is advisable to contact the member who donated the photo as to its use.