Design specs for banners:  

All file formats must have a minimum of 150 dpi (dot per inch) resolution at 100% of the final print size.
Images designed for the web typically cannot be used for printing as they have a low screen resolution of 72 dpi. Print images need to be created at 150 dpi or there will be a substantial drop in the image quality.

Color Mode:
All color artwork and/or images must be provided in CMYK (cyan, magenta, yellow, black) color mode.