Open iTunes and drag the audio files you'd like to add art to into the iTunes window. ITunes will import metadata automatically and display any embedded cover art.
Search for missing cover art images using your favorite search engine or a free Web-based music database (see Resources). Save any images you'd like to add to your audio files.
Select a single song in iTunes by clicking on its name. Choose "Get Info" from the "File" menu and click on the "Artwork" tab.
Drag and drop the file for the appropriate cover art onto the empty "Artwork" field. A thumbnail of the music cover art you chose will appear. Click "OK" to save.
Select an album in iTunes so you can add artwork to all songs in that album at once. Choose "Get Info" from the "File" menu. A message will pop up reading "Are you sure you want to edit information for multiple items?" Select "Yes." Drag and drop the cover art onto the blank "Artwork" field and click "OK." The cover art image will display with every song in the album you selected.
ITunes supports multiple images per audio file, so if you want to replace incorrect album art already embedded in a single file, you will have to delete the current image before adding a new one. Select the song. From the "File" menu, select "Get Info." Click on the "Artwork" tab. Click on the embedded artwork, and click the "Delete" button. Drag and drop or click the "Add" button to browse your files and embed the correct artwork. Click "OK."