[DrJJWMac]

My quick test shows no way of pasting in an image directly. Perhaps I am also missing something.

A suggestion otherwise is to save your completed sketch as an image absent the labels that you want to make in Greek or math font. Copy that image in to a canvas or drawing app, use LaTeXiT to generate your Greek or equations, and then paste in the Greek or equations on the canvas/drawing.

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JJW