Right click on the image you'd like to use, and a popup box appears. Select properties. The properties box appears. You'll see an address (URL). Click and drag to select the address (be sure you get it all, it will be everything beginning with http and ending with .jpg) and copy it to your clipboard. (Shortcut is CTRL-C)
Go to your DISboard and select Quick Links, then Edit Signature.
Place your cursor in the signature box. Click the yellow Insert Image icon. A box will appear asking for the address. Paste (shortcut is CTRL-V) the address you copied. The DIS will put the correct code and tags into your signature.
Save your signature.
Remember, be sure to use CTRL-C and CTRL-V to copy and paste. If you try to use the EDIT copy and paste buttons it might not work.