I have one of these in my house, because I seem to have quite a lot of photos of my family.
It's intended to display children's A4 sized art work, but I have a stack of nearly 50 photos inside, and I move the top picture to the bottom of the pile every few days. The photos are printed on 12"x8" paper, with a thick white border, as the aperture in the front of the frame is around 17cm x 26cm (approx. 7" x 10").
The frame can stand on a shelf or hang either horizontally or vertically.
I bought mine from Letterbox http://www.letterbox.co.uk/20670-12138/a4-single-picture-frame but I've also seen them at Amazon and Great Little Trading Company.