*** e2fsck
ext2fs_open2: Bad magic number in super-block
../e2fsck/e2fsck: Superblock invalid, trying backup blocks...
../e2fsck/e2fsck: Bad magic number in super-block while trying to open test.img

The superblock could not be read or does not describe a valid ext2/ext3/ext4
filesystem.  If the device is valid and it really contains an ext2/ext3/ext4
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>
 or
    e2fsck -b 32768 <device>

test.img contains `PNG image data, 148 x 31, 8-bit/color RGBA, non-interlaced' data
*** debugfs
test.img: Bad magic number in super-block while opening filesystem
test.img contains `PNG image data, 148 x 31, 8-bit/color RGBA, non-interlaced' data
*** tune2fs
../misc/tune2fs: Bad magic number in super-block while trying to open test.img
test.img contains `PNG image data, 148 x 31, 8-bit/color RGBA, non-interlaced' data
*** mke2fs
Creating filesystem with 16384 1k blocks and 4096 inodes
Superblock backups stored on blocks: 
	8193

