by Brian Yare.
What I did (see a topic I started only yesterday) was
1) copy the course moodledata from the old (1.9.15 in my case) site to the new site. This data was typically in directories numbered 01, 02, 03 ... , but I removed the backupdata folder before copying to the new site.
2) export all tables named mdl_course_xxxx from the new database using the 'replace' option.
3) edit the resulting .sql file (I used wordpad) to change the name of the moodle program files from its old value to its new value (I replaced /moodle_old/ to /moodle_new throughout the sql).
4) import this edited .sql file back into the new database.
I hope that this works for you. Obviously if your images were in questions then you need to edit the sql for mdl_question.xxxx.