When creating a promotion, each promotion type has an image than can be uploaded. Here is some information about each image.
Coupon and Flash Deal
The coupon and flash deal images can be used as part of the promotion, including text, QR codes, product shots, etc. The image size is 520 pixels wide by 266 pixels tall.
The typical Group Buy image supports the promotion and includes a product or brand picture. The image size is 214 pixels wide by 266 pixels tall.
The image used on information posts is a thumbnail that shows on the deal list. The thumbnail image size is 135 pixels wide by 69 pixels tall.