I am designing a website and want to have photos appear in the banner of the home page. The size of the banner is 900 x 120 and I want a photo with the same dimensions to fit inside of it. I've looked at different stock photo sites (e.g. istockphoto.com) and downloaded a few images for testing but am never sure what size to choose. When I choose ones that are large (e.g., 2716 px by 1810 px), they don't reduce that well to 900 x 120. When I choose ones that are small (e.g., 849 x 565), they don't stretch very well. Is there some "magic" involved in selecting the right image size? Is there a way to take one of these images, regardless of size, and make it the size I want it to be?
I'm a novice at this so am not sure how this works.