How to check if same files with other extensions are in a folder

I have a folder with a lot of videos and thumbnails for the videos. After wathching the video on Plex I delete it on the Web interface. So the thumbnails from the files stay in the folder.

Now i want to write a program that deletes all thumbnails, if there is no equivalent file.

Here is an example from "ls" of the folder:

PietSmiet - BATTLEFIELD HARDLINE - laufen, gucken, schießen # 11 - Im Nebel des Marihuna _ Deutsch Full HD - 1920x1080.jpg

PietSmiet - CITIES SKYLINES # 45 - Richtung 250k Einwohner «» Let's Play Cities Skylines _ HD60 - 1920x1080.jpg PietSmiet - GTA ONLINE # 89 - Die Hydra «» Let's Play Grand Theft Auto Online _ 60HD - 1920x1080.jpg PietSmiet - MEIN ARSCH BRICHT AUS «» PietSmiet probiert DiRT Rally - 1920x1080.jpg PietSmiet - MINECRAFT Adventure Map # 92 - Revolution of Adventure «» Let's Play Minecraft Together _ HD - 1920x1080.jpg PietSmiet - TTT # 171 - Wir brauchen Waffeln «» Let's Play Trouble in Terrorist Town Garry's Mod _ HD - 1920x1080.jpg PietSmiet - TTT # 171 - Wir brauchen Waffeln «» Let's Play Trouble in Terrorist Town Garry's Mod _ HD - 1920x1080.mp4