As a work around if you don't want to search for the images in your computer you might go to the quiz preview, right click on the image and select save image as. Then save to convenient folder. You could then zip and upload to your course the folder into a folder resource in your course. I usually put things like this in an extra topic at the bottom of the course and then set course settings so it doesn't show except when I am editing the course. The folder will be easy to find in your server files in the file picker.
Paula