If the cover art files are on the disk it is possible to import them as individual library items, like any other images.
Inside the library they can be organized by folder path, dimensions, file size, etc. You can create a playlist or smartlist of the images that don't match your criteria and use that list for determining which image files should be replaced.
If you don't want to import them to your main library you can create a new library just for the cover art files. Alternatively you could create a new view that shows only the cover art files and exclude them from the views that show other images. The inclusion/exclusion can be done by several ways (folder path, a library field value, etc)
I have imported (and tagged) my cover art files since 2004. I have custom views that can show the audio files and the related image files together (often I have also images of the back cover, booklet pages, CD, etc.)
EDIT
I just noticed that echamp1 mentioned embedded art. The system I explained does not work with embedded images. That is one of the reasons why I don't use embedded cover art.
However, MC13 has a tool that can move cover art according to the set options. It should be able to save all cover art images to a defined folder in addition to keeping them inside the audio files' tags. When the image files are saved to a single folder they are named using the [Album Artist (auto)] - [Album] rule. That should give enough information for finding out which albums have bad quality cover art when the cover art files are inspected inside MC.