Do you just "steal" them from websites or do you get them from sites like unsplash.com ?
Stocksy has some great photos that I use on occasion.
Unsplash is my go to. Especially with the integration with Craft plugin within sketch, makes inserting images easy. (and legal ;))
for premium, thinkstock (owned by getty...we have a subscription) for everything else, i use a few like Pixabay, morguefile, freeimages.com, sometimes compfight...
We have an in-house photographer. He's a beast.