Have yo got an Photobucket or Imageshack account?
If not get one. I've got Photobucket and it's great if a occasionally a bit temperamental about uploading stuff.
You 'll see on the Photobucket page an 'select photos and videos ' upload button and usually nearby is a small greyish box with a selection ie: 'computer, web' etc. Click the 'select photos' button and then click [I assume] computer and look for the file you want to upload saved as either a JPEG or PNG since it's best to make a copy of your original file and send this.
Once you locate the desired file click on it and it should appear in the long box at the foot of the page and click Open and it should start to upload. Sometime it doesn't error etc but if it does try again.
Once uploaded it appears in a window and asks you whether to give it a Title or edit it. Once you've done that and clicked the 'save to album' button it should appear. Here you can see some boxes with IMG code and IM E-MAIL type of stuff and if you want to upload it to the twoothy page click IMG code line and it will copy and save it.This is using Google Chrome so it might be different with another browser.
Then got to 2000AD page, sign in and then go to the reply or start new Topic page.At the reply window Press Paste and the image line should appear in the your reply window no need to put it inside image brackets. When you click to Post your image should appear in the Forum page all in it's glory.
That's how I doodle it anyway.