Ok, the first thing I figured out, this workflow won't work.
1) create shape
2) drop image on slide
3) select image and shape
4) Mask using that shape
5) select masked object
6) copy
7) open Image Tricks lite
8) "New From clipboard"
That won't work BECAUSE it appears that IT lite ignores the masking. When I do that, the ENTIRE image appears as if it wasn't masked at all. So will need to take another look at that. Also, I can see by your image that you are Exporting from Keynote, which I don't think will work from what I've been able to find. What SHOULD work is
1) create shape
2) drop image on slide
3) select image and shape
4) Mask using that shape
5) select masked object
6) copy
7) open preview
8) new from clipboard
9) save as PDF
10) open PDF in Image Tricks lite
11) save as PNG
But, that's THREE applications to go through instead of two. I'll ping the image tricks developers to see if they're aware of the issue.