Hard to tell exactly, but assuming this was taken in the USA it is 100% a harmless, nonvenomous snake.
Just in case it might help I tried to cropped and blew up your picture. It's kind of grainy but but might show a bit more detail. Well it doesn't look like the picture will get posted it's new size.
I agree; not close enough to really tell but it looks like a black snake. If you have a shed with access to under the floor let him go under there and snake and mice will be no more.
Looks like a black rat snake. It's hard to tell because the photo is at such a distance. If it is a rat snake, they are very beneficial to have around! They are also non-poisonous.
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