it doesnt have .jpg at the end, most of the time when "copy linking" from imgur it doesnt "add" the jpg or if you saved it as png, the .png thats all it is, you dont need to use discord, if you have the imgur link, just add .jpg, or if you saved it as png, then add .png
so the process simply is this
on your imgur, copy the link
on this forum type in "[img]YOURIMGURLINK.jpg[/img]" < -without quotes
adding the .jpg or .png depending on what filetype you uploaded to imgur