I figured out how to do this.
I edited 'questiontype.php' in * @package qtype_ddimageortext
define('QTYPE_DDIMAGEORTEXT_BGIMAGE_MAXWIDTH', 500); # was 600
define('QTYPE_DDIMAGEORTEXT_BGIMAGE_MAXHEIGHT', 330); # was 400
define('QTYPE_DDIMAGEORTEXT_DRAGIMAGE_MAXWIDTH', 190); # was 150
define('QTYPE_DDIMAGEORTEXT_DRAGIMAGE_MAXHEIGHT', 190); # was 100
The last two were relevant to my issue.