Add or Change the Album Art of Your Choice Manually

It is possible that some of your MP3 albums have no album art or you are annoyed with some photo showing in a song file in your pc and want to replace them with your own, you can manually add a picture of your choice.

To add album art to all songs in an album

1. Click the Library tab in Windows Media Player and then browse to the album that is missing art or which you want to change.
2. Using either Internet Explorer or Windows Explorer, in another window, find a picture that you want to use for album art (the picture can be in a file on your computer or on a Web page), right-click the picture, and then click Copy.
   
   The original picture can be in any of the following formats: BMP, GIF, JPEG, PNG, or TIFF.
3. In your library, right-click the album art box, and then click Paste Album Art.
   
   A copy of the picture is embedded into the songs from that album. The copy of the picture is automatically scaled to the proper size and converted to the JPEG format before it is embedded in the file. The original picture file is not modified.
   If you cannot add album art manually, verify that you have permission to modify the file. For example, right-click the file, click Open, right-click the file again, and then click Open File Location. In the folder, right-click the file, click Properties, and then clear the Read-only check box if it is selected.

Or You Can use a tiny software named Album Art Downloader hosted at Sourceforge.net