When 4images is setup to use compression (Settings -> Use GZip compression), the database backup compresses backup files into .gz files and thes files not being showed in backup list.
The fix is simple:
in admin/backup.php find:
if (is_file(ROOT_PATH.DATABASE_DIR."/".$file) && $file != "." && $file != ".." && preg_match("/\.sql$/i",$file)) {
Replace it with:
if (is_file(ROOT_PATH.DATABASE_DIR."/".$file) && $file != "." && $file != ".." && preg_match("/\.sql/i",$file)) {