Jagged Image Edge
This tutorial will outline how you can give your image a jagged edge. To start, open your image in Acorn, File ▸ Open.
Create a new layer, Layer ▸ New Layer. Using the flood fill tool, fill the layer with white.
Go to Filter ▸ Stylize ▸ Crystallize. Play around with the settings to achieve more or less of a jagged appearance. Click 'Flatten'.
Go to Select ▸ Make Selection from Layer, then Select ▸ Inverse. Click on the visibility eye of the white layer to hide it.
Click on the main image layer and hit the delete key. Deselect (⌘D). Make your canvas slightly bigger to really see the boundary, Image ▸ Resize Canvas.