Transparent PNG photo shape creator on iPad I have searched high and low looking for an app that will do a very specific thing.

I want to take a photo from my camera roll, apply a pre created shape mask to it (not freeform) and then save it back to the camera roll with a transparent background.

It appears that the iPad camera roll does not handle transparent .png files so well, it adds white where the transparency would be.

I have tried photoshop touch as well as a handful of other apps - but nothing seems to work. 

I know I can do it on a Mac, but I am looking for a mobile solution. 

Can someone please please help me.
This App will allow you to make parts of a photo transparent then save to your camera roll. You will have to draw the shape or use the simple tools to create the mask.  Works well for me as I usually want to remove the background. Not sure of the file format but they are transparent and are great to add to things like Keynote. 
https://itunes.apple.com/nz/app/background-eraser-for-ipad/id532187687?mt=8