It's best to set "view" to "Art and details" to see what is associated with the particular art. Then click on "Album" in the main tree. and you will get a list of all albums with art and all tracks. You could have duplicate tracks within each Album itself, or duplicate whole albums. I used dbpoweramp to rip my CDs and found it very good, except that if there was no Art available, if you used the scan facility, it takes ages, so usually I skipped that, and then edited the Art inside MM. Now that MM also has "Accuraterip", which I have not yet used, I suppose there is little scope for using dbpoweramp. But I liked dbpoweramp because it showed you up to three lists of tags, and allowed you to choose and edit, before you start ripping, so you can be sure that you have the right information. In the case of MM you have to edit each track individually, which although quite detailed, does not always make it easy.
To come back to the duplicates, if you are on "Album" view, you can see, at the right top corner, in the preview pane, under "Album" the total number of albums you have, and in the bottow left corner, how many files (tracks) you have in total.