This tool is use to is used to verify the data captured from an original laserdisk. The details below come straight from the MAME documentation. To be honest, 99.9% of MAME users will never need to use this program, but here's some details anyway.
ldverify [avifile.avi|chdfile.chd]
ldverify is a tool which walks through either an AVI or CHD capture from a laserdisc and ensures that there are no anomalies lurking in the VBI data.