pngcheck -vv ff-595.png
File: ff-595.png (9722 bytes)
  chunk IHDR at offset 0x0000c, length 13
    375 x 812 image, 32-bit RGB+alpha, non-interlaced
  chunk sRGB at offset 0x00025, length 1
    rendering intent = perceptual
  chunk iDOT at offset 0x00032, length 28:  illegal (unless recently approved) unknown, public chunk
ERRORS DETECTED in ff-595.png