Create a global variable called URL, set it to text, and leave the value blank
Global text URL = ""
Create a blank sprite (fill it with anything, color, etc...) I'll call it "Picture" for this example.
I don't know what conditions you want to use but, it's the events portion that matters here.
System> On start of layout > System > Set URL to "http://www.whatever.com/your_image.png"
System> On start of layout > Picture> Load image from URL (keep current size) or set to (resize to image size)
You'll be using sprite instead of the background object and you can change the condition to anything you want.
Hope this example helps...