I don't get to travel much, so I'm heavily dependent on whatever I can find online, at least as far as painting landscapes is concerned. I used to make some use of stock photos - the free versions have watermarks on them, but of course, one need not paint the watermarks!
I suppose it might still cause copyright trouble though, if you used the photo without paying. Mind you, I very seldom work very directly from a photo. In all probability, the photographer himself will not recognize his own photo in my work. A naughty trick: make a mirror image of the photo - it makes it less recognizable.
Anyway, nowadays I seldom do it this way, because I find most stock photos are not really suitable for my purposes. Some time ago I saw a YouTube video in which an artist kind of neatly encapsulated my own problem with stock photos: they're too pretty! He was explaining how he uses his own holiday photos as reference, and went through a whole bunch of them, explaining his way of work. He took some beautiful ones, and rejected one after the other as suitable reference: too much detail, or simply too pretty. As artist, he said, he's interested in shapes more than subject matter, and lots of spectacular landscape photos, beautiful as they are, lack the right kind of shapes.
I am of that same school of thought. Another YouTuber to follow is Ian Roberts, who has a whole channel dedicated to composition; he wrote a pretty good book on the subject too. It's all about shapes, and stock photos, as beautiful as they often are, frequently fail this test. I sometimes find something to paint in them by zooming in on some detail.
This of course means there isn't much too see, because when you enlarge a detail it gets fuzzy, but this is an advantage! I have noticed that almost like clockwork, my best paintings are done from bad, bad photos (at least as far as photography criteria are concerned). And this happens precisely because a "bad" photo allows me to see shapes first, and not get distracted by detail.
Nowadays I make quite a bit of use of Google Earth street view, an unlimited source of bad photos. It's not without its own problems: the camera is too high, so you look down onto the scene. One often needs to correct for this. Also, the lighting is sometimes bad when the photo happens to have been taken in the middle of the day. But one can use street view images without worrying about copyright.
For the rest, I sometimes get something done using almost random snapshots of whatever drew my attention (and once again, the bad photos often make for better reference!). An artist who greatly influenced my own art journey was a somewhat obscure blogger named Jeff Mahorney, who documented his entire learning-to-paint journey in a blog. He initially mostly did still life paintings form life, but eventually started using his own photos - and time and again, random snapshots of street scenes or people, which he turned into ever better and better paintings. Alas, he eventually quit painting and moved on to other things.
Anyway, I'm rambling, as usual. I'll stop now.
