You should look at Art4Apps: http://www.art4apps.org/ http://www.art4apps.org/ It's a library of images in the same dimensions and a uniform style, licensed un

You should look at Art4Apps: http://www.art4apps.org/ http://www.art4apps.org/ It's a library of images in the same dimensions and a uniform style, licensed under Creative Commons. They created it for developers of educational apps, but it could work just as well for worksheets!