Have not yet uninstalled IH and presume the 'Remove Image Handler from database' option does that for you. Once completed you would then see an 'Install' button on the right-hand side. Clicking the 'Install' button shoudl reinstall it.

Also, are you uploading images directly to the 'images' dir.? I ask because using the 'Clear image cache' option should not be deleting any source images.