I use Smugmug. Others use Photo Bucket and other free or cheap sites. Put the picture there, then just link to it.
The paid sites have better reliability.
Example:
To get a picture, copy it to your computer first. Then to your picture site. (Smugmug or where ever)
On your picture site, Right click on the picture and select Properties. Copy the entire Location link. Paste into your DU post.
Example:
http: //rc.smugmug.com/photos/79616711_5BquK-S.jpg (without any spaces)
It is bad manors to lift a picture or graphic directly from a site and put it directly on DU or wherever. It is called stealing bandwidth. Put it on your own server space first. Some sites take a dim view of this and have been known to replace the graphic/picture you are stealing with porn. Regardless of what others may tell you, don't do it.