ScanBizCards is the only iPhone biz card scanner with support for double-sided cards! When you take a new photo or import from a photo album, just touch “Snap/Import Other Side” to add a 2nd side. You can then scan both sides, or just one side. The cards list view shows double-sided cards as animated images showing each side in alternation. Oftentimes you may want to retain the back side visually but not necessarily scan it – your choice. You will find an example of a double-sided card in the Sample Images folder. Suggestion: if there is no back side, how about taking a picture of the person as the back side (just don’t scan it!) ?

You can watch the double-sided card support "in action" in this YouTube video.