Mass verify is an option that you can select when you define an image field. When it is selected, Verify displays images on the screen. There you can examine them and select the ones for which you want to create a field complement. (More info.)
Note that there is a more automatic way to trigger field complements.
If you want to mass verify image fields:
Open the Field dialog for the field you want to mass verify.
Click the Options tab.
Select Mass verify.
Tip: You can adjust FORMS sensitivity to changes in image fields.
You can also adjust how large the image fields are displayed in Verify. Do this in the Verify job options dialog.