Dalal : I don't think it's compatible with DirectCanvas, since AppMobi's backend is OpenGL, not HTML (and base64 strings are HTML-world only).
If AppMobi's object is intelligent enough to parse the base64 string before passing it to the directCanvas, you can have the image. Else, there's no possibility to inject images.
Since I'm not using AppMobi for the moment, somebody needs to do the test and report it back here, sorry.