The question that comes up is just who owns the original copyright. Just because it appears on any site on the internet does not, in any way, mean that particular site holds the copyright or has even received written permission from the legal holder of the copyright---the photographer, cinematographer, business or artist who actually took or made the photo, screencap or video---to actually display it on that website. Anyone wishing to download such material is walking on shaky ground in the legal sense by doing so, IMHO.
As an artist, myself, I am way too leery to put photos of my best work on line because I am fully aware of the vast quantity of people out there who would rip off my designs giving no thought to the fact that I put in long hard hours of work producing the piece and manufacturing it or photgraphing it, and that I expect to get paid for my efforts.
Some web sites grab any photo/screencap/video off the internet with the assumption that if it is displayed on that medium for all the world to see that it is free for the taking. Such is not the case. It is displayed for many people to see and enjoy only, not to be downloaded for someone to use in any and every way he or she sees fit. Displaying on a website is frequently done to attract business for the artist or photographer, and there are those who simply wish to share with others photos of what gave them joy. In any case the artist/photographer owns the copyright unless it has been transfered legally to a business or someone else.
Giving "credit" to the photographer isn't legal unless one specifically has a written agreement with that person to do so. IMHO, making any copies of anyone else's material is outright theft.