If you can upload then you don't need an account at imgur, but if you want to manage your old images then I guess you will need an account. There should be always an "image file extension" at the end of the link, when you paste the link here. Image file extensions = PNG, JPG, GIF, JPEG, WEBP.... You should not add it by yourself, the image link itself have either one of these.
WebP is a new image format invented by Google. If you convert a regular image to Webp image format, it will reduce its size a lot. So, a web page with webp images can load faster since the page size will be reduced. A memory card/Pen drive can store a lot of image files since the size of the images reduces. WebM is similar file format invented for videos.
There was no need to register or sign in - probably for an occasional visit - but if you wish to use this site for your pictures, you will certainly need an account there.
I have accounts at Makeagif and Imgflip, and you do have to register, but they are free, unless you want the deluxe versions, which are not necessary for my purposes.
Still can't get image file extensions. Used TinyPic on this one.
I think that Dan is the expert.
On my side, I tried to have a look and found a really cute gif:
http://imgur.com/gallery/l0MbSUH
It corresponds to a YouTube post:
There was no need to register or sign in - probably for an occasional visit - but if you wish to use this site for your pictures, you will certainly need an account there.
I've never tried Imgur.
I have accounts at Makeagif and Imgflip, and you do have to register, but they are free, unless you want the deluxe versions, which are not necessary for my purposes.