I've found a recent thread which partially deals with my questions -
- the reply here was to "place a button beside the field to 'zoom' it - ie: take the user to another layout where the image is full size, or another button to 'Select/Play' the field and it will open the file".
The latter suggestion is what I'm after but I'm unsure how to 'Select/Play' the field though...
You will need to have a button beside each repetition of the field (note that it is almost my duty to advise you not to use repeating fields.) Right click on the button text in layout mode and select 'Button set up'. Scroll down to 'Go to field', and specify in the dialogue box which field you mean, which repetition, and tick the box to 'Select/Perform'.
And the standard 'must-do' advice will also be to make sure you only 'Store areference to this file' whenever you are storing the image in the field.
I hope this helps,