Coming and Going, 12 x 24 inches, oil on linen
About half of my city paintings are done from photos. The other half are invented from scratch. (Or if you prefer, painted from memory. They mean the same thing to me.)
For this new painting, Coming and Going, I used a snapshot that I took a few years ago. It really does look like just a mindless snapshot, doesn't it?
As you can plainly see, I did take liberties with color, value structure, and editing. Photo references are just that; references. I use them for information about specific things, usually the construct of things that I can't easily make up, and perspective of its immediate environment.
I ignored color information for the most part. Usually the colors in photos are too...photographic, which looks nothing like reality so I don't rely on photos for information about color. The yellow-orange of the near trolley is the only thing that that I referenced. Even then, it's just a general hue direction, and not even close to matching the colors literally.
My color structure is made up, obviously. It's based on a blue near-monochromatic tonal structure. I added some warmths in the lit areas, and added a few subtle color notes such as the aforementioned trolley.
The value structure is more or less determined by atmospheric perspective. The closer the object, the darker the darks. The farther we go back, the lighter they become. (and the value range between dark and light narrows) So it's very systematically organized, though it may not look like it at first glance. The expressive brushstrokes and lost edges disguise the fact that it's logically laid out.
Also, I edited heavily. The pedestrian and the cars in the fore, the bus behind the trolley, background detail and cables... I make my editing decisions based on composition and concept. Will this element help me tell the story more clearly? or is it just fluff. If it's a necessary element, is it in the right place? If not, where should it be? Questions like that help me solve editing problems with logic.
The important thing to remember is that a photo reference is not something to be copied. If you were attracted to a photograph because it was so beautiful, what would be the point in painting it? I'd just as well frame the photo and hang that - much faster :-D
Kidding aside, I think it is important to be conscious of the reason why you are using a photo reference. In the end, I want my paintings to be expressions of my identity, not a painted copy of a photograph. I may need the help of photo references to do that, yes, but I never want to be a slave to them.