When you're creating landing pages within OSP here are some things to keep in mind for your background images. Images must be jpg/png/gif.
Background image guidelines
1. Backgrounds should be simple.
2. Backgrounds should not contain text or complicated graphics: these distract from your page elements and may not appear correctly on all device sizes.
3. Backgrounds can be any size you please, but we recommend 1440 x 900 pixels.