Currently, to transfer a macro that uses images, you need to export the images manually or use the backup feature to export all macros (the backup includes the images!).
With the next update, in addition to the current JSON macro export option, you will have the option to export macro plus all images used by this macro at once. All will be a single ZIP file macro that you can easily import on any other machine.
Actually, I recommend that you use the hard drive storage mode, then all images are directly on the hard drive, and you can just copy them to the new machine: