"Image Compare" does nothing

Hello all,

am trying to use the Image Compare feature. But even with the sample code it won't render on the page. Meaning , it does not show up at all in the source code of the page.

Plugin is enabled, the images have the same size, ...
What am I missing? Any dependencies? Tried to understand the js and php part of the plugin... but I don't. :)

Thanks for any hints,
g

Btw, what is the `?cache` part for?

```
[ui-image-compare]
[/ui-image-compare]
```