Now, if it is just one image then you can use the Attatchment feature to upload it and add it to the end of your post, or if it is an avatar you are using for yourself you can use the upload an avatar feature in My Controls.
However if you want to upload multiple images, for instance, a selection of signature images you have made for someone to choose from, you don't want to be making multiple posts with them in. You may already use a free image uploader, this is fine, unless it gets a lot of views and you run out of bandwidth, in which case an ugly "this account has exceeded its limit" image appears in its place.
If that is the case then may I suggest you use
You don't have to use it, but it is just a helpful suggestion from me
Also, please abide by the rules for signature and avatar graphics, the rules on sizes can be found in the Forum Rules