Essentially, the same rules as for Custom Covers still apply - i.e. a standard DVD cover should be 3240x2175 pixels, and MUST be 300dpi. Please check the main rules for non-standard sizes.
Additionally, for scans, there must be NO evidence of folds etc., on the spine, and there should be no evidence of curved corners. Any cover displaying moire patterns, or grain on images, or low quality text, particularly on small text such as credits and legal text, will be rejected. All dirt/dust marks must be removed, and the levels corrected so blacks are black and not grey.