[sciurius]

I suppose if I parse the file after the user has edited it and they have removed the ##image line, then I can just remove any image data associated with the given id.

I assume you mean "... have removed the {image...} line"? If the user removes an {image} line, the corresponding image data can be discarded (provided it is not used by another {image} line using the same id).

Adding an image is as simple as listing the name of the image file to include, so users can either write that themselves or I can add a simple option to add an image that lets them use a dialog to enter the data for the image (so that they don't have to memorize all of the supported parameters).

Right.

BTW it still would be possible to put an ChordPro file on the tablet that contains an {image src=...} but then it is completely the responsibility of the user to ensure the image file is also on the tablet, next to the ChordPro file. So w.r.t. files, MSPro would only need to deal with this very trivial case.