I am constantly searching for nice stock quality photos I can use for making Scripture Pictures and banners for my websites. I am learning to take my own pictures, and have made lots of graphics already with my own pictures (Deu 23:5 for example), but I do not have enough of my own to cover every need (yet). There has been a move in the past few years to make high quality, high resolution photos available for free use online. The camera photo in the title graphic for this post was from one of my favorite sites in this category, Unsplash. These are my favorites where I regularly find high quality photos (a Scripture Picture I have made with a photo from that site is linked in the parentheses):
No attribution required:
Painting masterworks of Western Civilization, painted before 1924, are in the public domain (see Acts 21:13 for an example). Many art history websites have virtual museums; check use and attribution requirements though.
Wikimedia Commons is another site to look into, although their photo quality and attribution requirements vary.