I think it would be a handy feature if there was a way to browse a gallery, select multiple images and with 1 click, add to cart. Maybe a checkbox by each thumbnail or something where a customer can select several images, then click add to cart. Once in the cart, have an option to select different quantities and sizes easily, maybe enter quantity 2, have 2 dropdown's appear where they can select the size for each. This might make it easier for customers to order multiple prints in different sizes.