I just received this question and wondered how other artists would respond. I also have included my response, but wondered if I missed anything. Perhaps the person who asked, will be reading and gain more info. Thanks
"I read that you use reference photos from Pixabay and Morguefile. If you use one of their photos for a painting, are you free to Copyright your painting, or enter it into a contest? Is finished painting considered to be an original or copy? How does one use others' photos without infringing on their work?"
My response: Online groups that offer copyright free photos have different guidelines. Visiting the two sites you mentioned and reading their guidelines is best source to have your questions answered.
Contests also have their own prospectus guidelines which also vary. Again, reading those would answer your questions. My past experience with juried contests is that they do not allow artists to use reference photos other than their own.
I also enjoy photography and for several years only worked from my own photos. In fact, I had a lower opinion of artists not working from their own photos. (And then there are the artists who think you ‘re not a real artist unless you work from life
The last few years, I have had less free time and am actually very thankful to carve out a few hours each week to paint. I use non-copyrighted photos as reference for convenience now. While not acceptable for juried contests and possibly not seen as authentic to some artists, I’m having fun and continuing to paint.