These are the bonus wallpapers you can find on the discs for the Dreamcast versions of Sonic Adventure and Sonic Adventure 2.
I have converted them to PNG format, and where possible, I've also edited the originals to stretch them into larger widescreen resolutions - 1366.768 and 1920.1080. Please note, not all of the images were easily expandable, so every resolution might not be there.
or download only:
1280x
1366x
1920x