what is exactly the trouble? If you are using Dropbox follow the steps.
[FONT=ArialMT, serif]Step 1:[/FONT][FONT=ArialMT, serif] Drop a file into the Public folder.[/FONT]
[FONT=ArialMT, serif]Step 2: [/FONT][FONT=ArialMT, serif] Right-click/control-click this file, then choose Dropbox > Copy Public Link. This copies the Internet link to your file so that you can paste it somewhere else.[/FONT]
There are two ways of attaching a photo I think. Apparently you are using the online one. You can use the offline one, by first going "Advanced". Then instead of using the Image icon which is for attaching a pic in a URL (and I think you are currently using it), click the Attachment icon (at the right side of the Smiley icon [in Advanced mode]). Then a window (or new tab in some browsers) will pop up. This way, both online and offline options are ready to choose. The lower box is for pasting a URL, while the upper box is for placing the address on your local drive (it has a Browse button as well).