Images or other attachments in the answer feedback html for Essay questions will not display during the review of a quiz attempt. This appears to occur because of a bug in the Moodle code for this question type. The 'component' and 'filearea' names in the 'quiz_rewrite_question_urls' call in the 'print_question_formulation_and_controls' method in $CFG->dirroot/question/type/essay/questiontype.php do not match the names used in the 'import_or_save_files' call in the 'save_question_options' method in the same file. Looking at the code for other question types, it seems as if the 'quiz_rewrite_question_urls' call should be modified to follow the component and filearea names in the 'import_or_save_files call' (i.e. 'question' and
'answerfeedback' instead of 'qtype_essay' and 'feedback'). If this is done, it seems to fix the problem.