This tutorial will explain how to do said steps using two popular image hosting sites, Photobucket.com and Imageshack.us. The steps are separated into General, Photobucket and ImageShack therefore which ever service you choose you can quickly reference the information needed.
General
1. After creating your piece of work save in a common file format such as *.png, *.jpg, *gif, etc. as Paint.NET's native file format (*.pdn) is not recognised by any other program or website other that Paint.NET.
2. Connected to the Internet, got to either Photobucket.com or Imageshack.us. Once there choose whether you wish to create a free account or upload there-and-then.
Photobucket
3. Once registered and signed in click 'Browse' and search for the file you wish to upload. Click Upload.
4. After uploading you have four different link options underneath the uploaded image, the useful ones are as follows:
Direct Link - this is what you use for avatars. In your Forum Profile, paste that link into the 'Link to off-site Avatar' field.
IMG Code - this line is used for using your image in a post and signatures, this will make the image appear full size in your reply and your signature block.
Thumbnail - for clickable or otherwise (when clicked it will send you off to the full size image) in your post, then select the desired image by it's adjacent tickbox, scroll to the bottom and find Generate HTML & IMG Code, and select the code within the third text box. You may generate code for more than one image at a time if you wish.

ImageShack
5. Once registered (or not if you choose to go for an on-the-fly upload) click 'Upload Image' on the left under the Action heading and search for your desired file. If there is no other online modification to do click Upload.
6. Following the upload, click the small 'i' icon (
) next to the thumbnail of your newly uploaded image. In the dialog that appears you have similar options to that of Photobucket, the useful ones are as follows:Forums - this line is used for using your image in a post and signatures, this will make the image appear full size in your reply and your signature block. Highlight the top line and copy that into your post or appropriate Profile field.
Direct - this is what you use for avatars. In your Forum Profile, paste that link into the 'Link to off-site Avatar' field.
Thumbnail size, Forums - Use this line for if you wish a thumbnail of your image to appear in your post; once clicked it will take you to the full size version of the image. You will only want to untick the checkbox 'include details' if you do not wish for the date of the picture to appear in your post.

Any other linking options from Photobucket or ImageShack are either not needed here or use HTML which can't be used in the Paint.NET Forums.
7. For posting your images, whilst in possession of your image's URL, simply insert it into a set of image tags, like so: [i][size=85]URL[/size][/i]
The closing tag must include the slash to denote the end of the command. Also, if you ever need a quick reminder of tag use, you can always hover your cursor over the relevant button above the field where you write your post reply.
For clarification or further reading of any BBCode used in this tutorial, do refer to the FAQ section, found here: faq.php?mode=bbcode
EDIT: added information on using the above codes for signatures, for some reason I missed that out despite it being one of three reasons for this tutorial.
EDIT 2: added instructions for the application of code within the post - so, as well as how to get there, it now details what to do with it.
EDIT 3: updated a few aspects of the tutorial.
EDIT 4: covering all edits from hereupon, usually for host-side updates to the process, additional information, or for tutorial re-formatting.
























