Hmm, you are working with IrfanView, then ...
within Irfanview open the dialog for searching files by pressing [Ctrl+F].
Enter a fitting file search mask, for example *_1.jpg
Enter a root folder.
Set the option to search in the foldertree.
Start the search.
Display the result as "Thumbnails".
You may apply the search engine of "TotalCommander" or "Windows Explorer", ...
both understand a search mask like ... _1.jpg;_2.jpg
.... or on the DOS commandline ...
M:>DIR /S _1.jpg;_2.jpg
See dialog "Mp3tag/Extras/Options/Tags" ... there you may add the filetype "*.jpg" to the list of filetypes, which Mp3tag should show; afterwards refresh Mp3tag list view.
Maybe you can reduce the amount of duplicate exported cover files this way:
within the action "Export cover to file" ...
do not check the checkbox for creating duplicate files.
DD.20160315.1919.CET
This may help to reduce duplicate cover image files ...
Action "Export cover to file"
Formatstring: %_filename%'.'%_cover_type%
Export duplicate covers: no
This works only if the files in one folder do not have embedded art with different properties.
Otherwise, one picture file per version will be created (and numbered).
So it is worthwhile to check the folders where there are duplicate files although they should not. The duplication means that something is different.