You'll need to post your pictures on a web server somewhere. My Cox cable account comes with a personal web space, which is where I keep mine. You can also use a free service like photobucket.com. Follow the instructions for uploading your picture to whichever site you're going to use.
Once your picture is online, in a separate browser window, browse to it. Highlight everything in the white box at the top of the brower page (where you type the internet address), and press Ctrl-C to copy the address of the picture.
Now, back in the DIS post where you want to put the picture, click the yellow button that has a picture of a mountain. This is the "insert image" tool. Clicking this will open a window that says "enter the URL of your image. Click in the white box and press Ctrl-V for paste. Click the OK button and your picture should be in the post.