There used to be the option to upload photos via a web URL by default, but now it only seems to pop up semi-randomly, and if you switch from the URL option to the normal photo uploaders, you can't switch back to the URL option (it's been that way for me for quite a while, anyway).

One thing I have noticed though, is that if there are already images uploaded and I click the 'Add photos' option, up springs the URL option...but only one field, so it would end up being a bit of a process and may include some trial and error. 

If you really need to upload from a website, it might be easier to use Turbo Lister, as that has the option in there by default. (I think.....it's been a while since I used TL).