Read extra lines from PNG file (Avast reversing challenge at Security session 2018)

png_extender.py

import png

rdr = png.Reader('E3EA158BA24F4D9573C04A0687F47F3BA3DB096ADA14729ECF7574678733E8AF.png')
w, h, pixels, meta = rdr.read()

# read returns width, height, pixels as Map and metadata
# (600,
# 790,
# <map at 0x7ff98c07e908>,
# {'alpha': False,
#  'bitdepth': 8,
#  'greyscale': False,
#  'interlace': 0,
#  'planes': 3,
#  'size': (600, 790)})

# Increase the height to 800 pixels to view the secret message
writer = png.Writer(width=w, height=h+10,
	planes=meta['planes'],
	bitdepth=meta['bitdepth'],
	interlace=meta['interlace'],
	alpha=meta['alpha'])

with open('extended.png', 'wb') as f:
	writer.write(f, pixels)