vdiff

/vee'dif/ v.,n. Visual diff. The operation of finding differences between two files by eyeball search. The term `optical diff' has also been reported, and is sometimes more specifically used for the act of superimposing two nearly identical printouts on one another and holding them up to a light to spot differences. Though this method is poor for detecting omissions in the `rear' file, it can also be used with printouts of graphics, a claim few if any diff programs can make. See diff.