Something that Might Confuse you
If you select a whole drive in TreeView (left section of screen), it displays thumbnails of all the images on the drive. In case you were wondering, that's what "deeply" means in some of the info boxes and suchlike: all the images in all the folders.
So take care about selecting an entire hard drive; even though PhotoGrid is blindingly fast at what it does, it does take some time if you give it thousands of files to look at.

Fortunately, you do get a warning that a big job is underway.

And as the information box indicates, it's easy to stop the search.
Entire Drive Search