I use some photos from stock.xchange (www.sxc.hu/home, it changes its name to free.images.com) for pictionaries, etc; but you have to register to download them. You can find some backgrounds and images for your worksheets there, too. some photographers may ask you to give them the photo credits.
See this options, for backgrounds with the shape of a notebook, for instance: (NOTEBOOK SHAPED BACKGROUNDS) http://www.freeimages.com/browse.phtml?f=search&w=1&txt=sheet&p=3
More photos on: www.publicdomainpictures.net , see for example: (FRAMES) http://www.publicdomainpictures.net/hledej.php?hleda=frame&x=0&y=0
You can download packs of thematic images or art from media militia for free (freebies) to use them as background: www.mediamilitia.com/category/freebies/
Tip! Don �t download the packs that only contain .EPS o .AI images, unless you use photoshop or adobe illlustrator. You can download .PNG images, that you can use with any computer program. See, for example:(101 RIBBONS AND BANNERS) http://mediamilitia.com/3d-elements-ribbons-banners-pack/
All these images are public domain (PD), it means that they can be used without restrictions, even for commercial purposes.
I hope you find this information useful for you! ;)
Cheers!