How to insert album cover art on music files?


I have searched the net for answers and I have not found any feasible answer to the question:
"How to insert album cover art on music files?"

I have about 4-6TB of music on external hard drives. Much of this music came from live broadcast sources through the years. I also have much HR music recorded from various on line services recorded via a HR Tascam recorder then transferred to the hard drive.
How can I insert a picture into those music files on my hard drive? Low rez sources such as iTunes, or mp3 conversion is not an option.

ozzy
128x128ozzy
Do any of these cost money to download?
And I already have the music on the hard drive and most are in the wav format.
ozzy
Picard can be downloaded for free. Very powerful and able to auto tag and add album art automatically in many cases.

if you already own and rip using dbpoweramp the editor is included.  Otherwise a nominal cost to download. 
Yes the dbpoweramp editor has an option to select image files you store on a directory on your computer. 
Picard might also not sure.  Never tried. 
Ozzy wav format might be an issue for what you want to do. Wav format is not inherently flexible with tagging. Never tried Wav with these tools. I started with wav and used dbpoweramp to bulk convert wav to lossless flac which is very flexible with tagging.  If tagging files with art and other info for usability matters to you I would suggest converting to flac.