First off, DHC requires that the pic be under 1 mb so you need a way to resize your pic as most cameras take 3 MP or larger. A good way to do it is with a software program such as Paint.net (free) or a link to a photo editing site and storage such as Photobucket (free).
After you have either resized your photo to under 1 mb and saved the resize to your file you click the post reply on DHC, click on the 'upload attachment' option at the bottom, click on the 'browse file', select the resized pic file from your computer and 'open', click on 'add the file', and after it downloads the file to the area on the bottom of the post, you position your cursor where you want the pic to go and click on 'place inline'. The pic will be positioned properly after you "submit" your post.
If you are using photobucket, you upload your pic to photbucket, left click on the "image" box which then 'copied' the file, go to the post reply area in DHC thread and position your cursor at where you want your pic to go, then right click and the pic will download and then you "submit" your post.
Try it as a "test" in this post to get the hang before you waste lots of time writing a reply and losing the info because you erred.
If you decide to download Paint.net, you select the image, then to resize your image you go to 'image', click resize, select 50% or whatever gets it under 1mb, click resize, then save to file as your named file with an extension so you don't replace the original.