What high-level problem are you trying to solve?
When I design a form with a default image that is loaded to the widget for annotation, it is possible for the enumerator to accidentally replace the default image if they are not paying attention.
They then need to discard the submission and start again or potentially don't realise what they've done and submit bad data. (This is not theoretical, it is happening to me and all I can do currently is put big red warning notes in the label)
Stretch: If someone is annotating and saves it, but realises they made a bad annotation, could there be a 'reload' button that could force the dynamic image to be reloaded to start again?
Any ideas on how ODK could help you solve it?
If the 'Take Picture' and 'Choose Image' buttons were suppressed, and the only option was to annotate the image, then this error would be prevented.
This would be an appearance for the widget, similar to annotate, eg no-capture, no-choose would each suppress one button so the appearance value would be annotate no-capture no-choose, or a single annotate_default to apply all three flags.
I think this is possible and perhaps not that difficult (‽) as currently annotate is an appearance that "unsuppresses" a button, and there was recent discussion about changing visible buttons for sound recording: