As far as I know, the forum's image proxy is limited to GIF, PNG and JPG (probably also JPEG).

Someone should setup an image host dedicated only to Bitcointalk, that converts all images to a working format.

JPGs and JPEGs are the same file format. JPG and JPEG both stand for Joint Photographic Experts Group and are both raster image file types. The only reason JPG is three characters long as opposed to four is that early versions of Windows required a three-letter extension for file names.

Source: https://www.adobe.com/creativecloud/file-types/image/comparison/jpeg-vs-jpeg-2000.html#:~:text=JPGs%20and%20JPEGs%20are%20the,letter%20extension%20for%20file%20names.