The image link guidelines have been updated recently, see the new text below or in the wiki.

Please adhere to these guidelines when adding images on-site:

Do not 'hotlink'. Hotlinking is putting in a link to a website that DOES NOT allow just anybody to upload images to it. (e.g. Google images, Wikipedia, any website other than an image hosting service)
Only link to image hosts. The accepted image hosts can be found here.
Do not link to very large images (this does not apply to screenshots). Most of the above mentioned image hosts automatically resize uploaded images to reasonable sizes, so this should not be an issue.
Use of any image hosting service is allowed for forums. However, try to avoid using images due to their new image storage policy (dee for more details)
Sites/blogs such as Tumblr are not considered image hosting services and as such should not be used for posting images.

Please adhere to these guidelines when adding a link to game cover art:

Only link to an image of the games front cover art.