A
wiki article can have files attached to it, normally images, to better illustrate your point. There are two methods, the simple method and the advanced method.
Big Mike has created a video which shows both the simple method and the advanced method, step-by-step.
With the simple method, you simply click the paperclip icon or click Manage Attachments while editing the wiki article, and upload the image just like you would in a normal forum post. The image(s) will appear at the bottom of the wiki article as thumbnail(s) and can be expanded when clicked. The disadvantage to this method is you cannot control the location of the image, so it is not near relevant content. The advantage to this method is it is simple and easy.
With the advanced method, you must first upload the image to the wiki directly into the
wiki images namespace. This process is very similar to creating a new wiki article. First, the article name within the wiki images namespace is actually the exact filename you want to use to refer to your image from other wiki articles. Second, you attach the image and a short description of the image within the wiki article body, again referring to the article within the wiki images namespace. Last, once that is saved, you can go back to a regular wiki article (outside of the wiki images namespace) and reference your image, control its placement location within the article, and add a caption. The wiki system will generate a thumbnail version of it that when clicked will open to the full size version.
Wiki How-To's 
