Image Target Mis-interpreted

Hello, 

I am writing you to ask for a help: During our project we had to insert 5 images as target images. Those images should be "similar": they all should share the same structure and present a common element. The distinguishing element is the background.

I have used ranodmized positioning of different geometrical shapes in the backgound.

You can see the images in the attach.

I tested them on the editor and all of them got a 5 star measure. However, once loaded in the application on unity, only three of them are recognized, the other are misinterpreted: in particular the one with hexagon and the one with triangules are minsintepreted as the one with the stars.

I have also tried sevela different images (stars with more points, diamonds, hands, cubes, ...) but no matter what I try I can get at best three images right instead of five.

Can anyone please help me understand how to solve this? Are there anywhere 5 background patterns guaranteed to work?

Thank you all very much.