EDIT -
Sorry to be a pain, my artwork was showing and now it’s gone again? I really wish this could just be a simple button that lets you select art in the folder where the film sits.
Let me explain what i’m doing any hopefully someone can tell where i am going wrong. 
So i have my harddrive with a folder called Vipco. inside this folder i have my ripped Vipco screamtime collection. each film is in its own folder and here is an example of a folder name -
City of the Living Dead (1980) {imdb-tt0081318}
inside this folder i have the film which is titled as follows -
City of the Living Dead (1980) {imdb-tt0081318}
then i have the same dvd cover art and have names each one with several different styles that the internet tells me to use, none of which are showing up (one did for a few hours and its gone back to plex’s original art and i can;t get mine back?)
City of the Living Dead (1980).jpg
City of the Living Dead(1980).jpg
Poster1.jpg
Poster.jpg
So i go into Plex to Settings/Agents then i have a top row of options - movies, shows, artists, albums and photos and then below each i select ‘local media assets’ and put that at the top of each list in the catagories for movies and shows. (that’s all i use plex for).
after that is done i go to settings/manage/libraries/ i find my Vipco library and go to the right an select Edit library/advanced and i get the following options.
scanner
agent
visability
i’ve played with each combanation of the following options above but have no idea what these should say? but no matter which i choose in thier respective drop down boxes, after refreshing the metadata on my vipco library, the art simply changes back to what plex offers.
below these options i select (by ticking the box)
Use localized posters when available.
When scanning this library, use local posters and artwork if present.
When scanning this library, prefer embedded tags and local files if present.
each is selected. i then go back to the main page of plex, go to my library, go to the Vipco folder and refresh the metadata. nothing changes. so i then go into the individual film (in this case city of the living dead) and refresh the films metadata and it will either change to a odd landscape screen shot of the film or go back to a regular portrait box art that plex offers?
somehow i managed to get my dvd cover art to show up around 1am this morning, i was super chuffed. came back today and it had reverted back to the plex art? 
If anyone can see what i am doing wrong here, i would love to have a proper fix for this. i just want to choose my own art, and have it stay in my plex so i can enjoy seeing the art that i grew up looking at. 
Thank you again for your support and help with this.
((Plex staff if you are seeing this, please consider just having a button for people like me who aren’t savvy with all these options that just lets me make the program choose the art i stick in the folder next to my movie, that would help so much.
))