http://photobucket.com/
http://www.imageshack.us/
http://www.tinypic.com/
http://www.theimagehosting.com/
There are many more image hosting sites out there and most of them are free.
Art sites like Deviantart, SheezyArt, VCL, FurAffinity, and others generally do not allow direct linking, so you will have to post it as an URL rather than as an image. Hotlinking images to embed them into a post often use a lot of bandwidth from the site they are linked from and drains their resources. Some sites will display errors when linking. Hotlinking and embedding images from privately owned sites, unless you own the site, is prohibited as they do not have unlimited bandwidth and it is considered stealing. So please use one of the image hosting sites above to post and embed images into the forums.
The code for embedding images is
[img]http://www.yourimagehosthere.com/image.jpg[/img]
The code for urls is
[url]http://www.yourimagehosthere.com/image.jpg[/url]