Resizing map annotations to fit custom button / views in the annotation

Hi all,

I'm trying to add a thumbnail to the annotation when its clicked. This works well on Android. The annotation resizes itself to fit the image, but on the iOS simulator it doesn't.

Is there a way to dynamically resize the annotation?

Had a look at the documentation and there doesn't appear to be size properties - so if the above is not possible, how can I create a custom annotation to override the system one?

Thx, Ken