I've considered for a little while now and the solution I came up with for myself was as follows:
If referencing a specific image, try to contact the image owner and ask for permission to reference with a promise to give credit and link back to the original image. (Obviously I don't then reference images where the creator has made it clear they don't want anyone to use their work).
Otherwise, for commissions or in general, I tend to look up a library of images for the subject type I want to paint and create something based on the collection of images I see, rather than any individual piece. Eg When painting a dragon borne, I google searched that term and created something based on an "average" of the images that came up.
you can use references as long as you dont sell the stuff...if you practice a lot,it will build your muscle memory,next time you can build things yourself..
there are rules tho,that using reference is ok,to study shape and lighting mostly,but not to exactly copying it.for example if you draw a woman face from google for commercial product,you only draw a portion of her face that you need (like shading,mostly on the nose since nose are so hard to draw) and draw everything else from your muscle memory and anatomy reference.
if you want to start using reference photo,i suggest to see anatomy reference for a start, it will help you learn a lot
And what about if I use one of them as reference for a X commission as an example? I mean only use that pose inspired on that Y image and other parts will be made by pure creativity (no copying obviously)? Note: I don't do commissions yet, It's just an example.
tracing can be done manually and digitally,manually we just print it out an line it on our paper.
copying,as far as i know (i dont know if art thief nowadays can be more creative than me) can only be done digitally. it is literally just selecting one part of what we cant from reference and copying it right inside our piece.it is definitely prohibited...
while landscape/environmental artist do tracing to create landscape from imagination (and there has been talk about whether it is ethical or not),for portrait artists this is strongly not recommended at all.
Thank goodness that I learned to never trace So I feel a bit relieved and less worried now. Thanks for sharing ideas I used Google Images searching for any rabbit/bunny image as reference for this: Forrest The Rabbit