[est]

You can always change that to

    =image("http://targetname/1.jpg")   
    =image("http://targetname/2.jpg")   
    =image("http://targetname/3.jpg")

[robzyb]

But what if 2.jpg doesn't exist? Or is a trivially small file?

The advantage of the querystring-method is that you can just find one suitable (i.e. huge) file and force Google to pull it down many times.