“What is it about that street?”
Artists will often tell you to use photo reference (including myself) but also, in the same breath, tell you not to copy it. The question that inevitably comes after is “when does it hit the point when you are merely copying?”
The degree of how much you take from reference depends on what is required for your artwork. It is absolutely impossible to dissect every individual case. It is, however, poor form by the “artist’s code” to merely copy a photo. In any case, it is very tempting to do so, similar to looking at the back of the textbook for the math answers instead of actually doing the thinking.
Still, at what point is it “copying”? There’s one simple way to always avoid a case where you merely copy. It’s very easy; you create an opinion based off your reference.
When you look at photo reference, it’s easy to fall to the trap of using it as an answer to “What does this street look like?”. While this is a perfectly legitimate question (nobody’s brain can possibly have perfect knowledge of the subject matter they draw), copying photographs will merely give you a lifeless result.
As artists, we have to do better than that. We can change the question to “What is it about that street?”
That’s the difference. The latter question inserts YOUR opinion on the matter. You are no longer occupied with the objective reality of the reference. You can now bring your own reality into it.
Perhaps a photo has the colours you want but nothing else. Perhaps you like the way the buildings look but not the lighting. Perhaps you love the composition but it just might be better by removing a few things.
No matter what you choose, your opinions will naturally stray away from the reference itself. Suppressing your own feelings on what you see is a good tool for practice if you’re looking to understand objective reality.
Beyond that, you must learn to be judgemental. Understandably, that’s a trait that isn’t seen in a positive light when it comes to people but our entire existence as artists is so our audience can enjoy our interpretations of life, not what the camera tells them. It’s as if all your fans are asking “What do YOU think?”
A photographer is limited by what can be seen in the realm of reality (barring photomanipulation). We, as artists, can portray whatever our imaginations can conceive. If you want a giant robot in your picture, you can damn well have a giant robot in your picture without paying millions to construct it in real life!
On a related note, this is also why you should avoid copying other artists’ answers to artistic problems. A professional artist’s style is their signature; unless there’s some sci-fi machine capable of copying their DNA and life experiences, any attempt to imitate will look contrived. It is very easy to tell when an artist is being honest and when they’re not.
Trust in yourself.