where to call wwwLoadImageIntoTexture

Hi guys, simple question here that is stumping me:

I want to use wwwLoad to pull an asset and assign it to a target when the target is recognized on screen. Where do I use the wwwLoadImageIntoTexture function? Does it belong in the UI javascript? Do I integrate it into the event handler .cs?

Any help would be amazing, thanks.

I usually will set a flag in my UI (OnGUI) functions and have Update handle such things, because OnGUI is called several times per frame and Update just once.