first you need a website to host the pictures. www.photobucket.com is a great one to use. For one-offs, www.imageshack.us is also a good place to use.
Upload your pictures there, and when it's done, you should have the url of the picture. It'll say http://blah...blah...blah. You need to highlight and copy the entire url.
Then when you're posting on the DIS, paste the url that you've copied.
Make sure you have
at the end of the url, without any spaces between the and the url.
Photobucket usually gives you the url with the [img]'s already attached. You just need to paste it on to your post and voila... you've shared pictures!
Just don't use Yahoo as the site to host your pictures. When you enter the URL the picture will not appear in the thread, just a link to its location. It works, it just doesn't show your picture in the thread where you are posting.