Pretty straight forward idea. This would open up flexible tracking for Picture frames with glass surfaces. By tracking only the frame (with a transparent empty center) it will ignore any potential glare or lighting issues and track cleanly. I am sure it can benefit other applications but this is the most obvious that comes to mind.
ZapWorks already supports png target images. Here’s an example in Studio below, using a picture frame as the target:
The 3D phone model would be tracked to the physical version of that frame image. However, it’s important to note that tracking from this would not be ideal, as it makes for a pretty poor target as it would lack contrast and sufficient detail. This video explains the type of things to look out for when designing target images.
Although the glare that occurs on shiny surfaces can cause loss of tracking, the use of a poor target would result in equal tracking issues.
Hope this helps. Let me know if you have any other questions.
All the best,