Dzug2's response seems to assume that you want the URL of the original image, in its original location. But, if I read your question correctly, you want a URL for the resized image, which is currently on your desktop.
Go here:
http://tinyurl.com/65v5uqh
Click 'Browse'. Navigate to your desktop and double-click on the image file. Click 'Upload now' (and enter the security code you'll see). Your image will then be uploaded to the web. Click on the link labelled 'Direct Link for Layouts', which will highlight it. Right-click and select 'copy. Go to where the link is required. Right-click and select 'Paste'
Chris