No workaround - download the PDF with images.
Moodle assignment submissions - JPEG files
Currently if a student submits a JPEG file to a Moodle assignment, the PDF converter is not able to process the file. Staff are therefore not be able to provide feedback by annotating the document.
Staff can download the file to view it. To provide feedback, staff may wish to use an alternative feedback method e.g. upload a Feedback file or enter comments in the Feedback comments text field - https://wiki.ucl.ac.uk/x/RawpAg
Moodle assignment rubric does not scroll on tablet or mobile devices