Remving thumb files from content_image selector

[Dr.CSS]

The only way to get thumbnails is to look at the images in image manager or uploading them using image manager, go to file manager and upload them there, you can look in the settings of file manager for Show thumbnails
Enabling this will show thumbnails of image-files if they exist, and will hide the actual thumbnail-file. Disabling will simply show all files.
untick this to see the thumbs and then you can delete them...

I haven't used image manager in like 4 years I always use file manager...