I have new solution for this old problem. It is similar to ohrenkino's solution above, but it works only in the the directory of the current file and you don't have to work with text editors once you have set up the tool.
You have to create a .bat file and a Mp3tag Tool. To create a bat file, create a .txt file and rename it to .bat
Name: C:\Users<username>\AppData\Roaming\Mp3tag\rename picture to folder.bat
ren *front*.jpg folder.jpg
ren *cover*.jpg folder.jpg
ren *.jpg folder.jpg
ren *front*.png folder.png
ren *cover*.png folder.png
ren *.png folder.png
ren *front*.gif folder.gif
ren *cover*.gif folder.gif
ren *.gif folder.gif
ren *front*.bmp folder.bmp
ren *cover*.bmp folder.bmp
ren *.bmp folder.bmp
Name: Rename picture to Folder
Path: C:\Users<username>\AppData\Roaming\Mp3tag\rename picture to folder.bat
The bat file will only rename one picture of every filetype. It looks first for a file with "front" in the name, than for a file with "cover". If both not found, the alphabetically first file will be renamed to folder.
I have included several filetypes to have one tool for all files. But you can also split this into different tools or use only jpg files. No filetype will be changed and only files with the specified extentions (.jpg / .png / .gif / .bmp) will be renamed.
I'm new to the cmd operations. So please correct me if I made a mistake somewhere. But it seems to work perfectly from a few test I have done.