Hello,
I am using RSync to clone my mac itunes library to my Plex server.
I also use applescripts (from here) to save the album art inside itunes album folder. Everything is beautifully organized.
Unfortunately on Plex Music, the album covers are downloaded from somewhere but I only want the covers saved in the album folder. Nothing Else for the album covers.
Nothing in this Plex guide mentions that : https://support.plex.tv/hc/en-us/articles/200265296-Adding-Music-Media-From-Folders
Thanks for your help
Nic
The way I have found to make it work is to reorder the “agents” Plex uses for gathering metadata. Several obscure TV shows and foreign movies ALWAYS are matched wrong. But when I moved up in the Agents que the item “local media assets” this seems to force Plex prefer my local image over some external sourced image.
Hope that helps.
Rob, i just deleted my music and reordered the agents to have local media on the top for the artists and albums … but it doest not change anything… it is getting the cover from the web i think. 
My cover is inside the folder of an album and it is the name of the album. example : AC_DC - Back In Black.png . or The Best Air Guitar Album In The World Ever II.png
Plex will only recognize certain filenames. For albums, the artwork files must be named album.[ext], poster.[ext], default.[ext], cover.[ext], or folder.[ext]. The [ext] can be jpg, jpeg, png, or tbn.
Here’s a more thorough explanation of the artwork names Plex will recognize:
Thanks to both of you the problem is solved. I used this script in itunes : http://dougscripts.com/itunes/scripts/ss.php?sp=savealbumartjpeg
So like beckfield advised I saved all covers in cover.jpg then I used “Local Media Asset” on the top of every agent in albums and Artists.
I deleted the library and reinstalled it.
It ran a scan and the problem was solved.
NB: The only tiny issues was that sometime Plex used another cover because in iTunes the artwork as front and back covers. I deleted all back covers in itunes and it is perfect now.
Thanks