There are tons of wallpaper sites with high quality images. There are also a lot of dog picture sites with very high quality images of all sizes, if you just want to experiment and test your software and website.
Welcome to http://www.myphotowizard.net
where you can edit images, make a photo calendar, add text to images, and do much more.
When you know what you're doing it's called Engineering, when you don't know, it's called Research and Development. And you can always charge more for Research and Development.