A TimThumb error has occured

The following error(s) occured:

The remote file is not a valid image. Mimetype = ''/home/users/p/popracy/www/239584/html/thumbs/cache2/timthumbm32glf

Query String : cat=galeria_uzytkownikow&src=http://img.popracy.pl/galeria_uzytkownikow/1367/img_20200929_103845.jpg
TimThumb version : 2.8.14