Based on the PNGsuite.
The following set of images show some more uses of ancillary chunks. The first row contains images with timestamps or,
compressed or non-compressed textual comments.
The leftmost block of 16 images (3 rows) is again the reference snapshot. The rightmost block should look identical.
If it doesn't, your software does not correctly handle some of these ancillary chunks.
The following images were used (left to right):
cm0n0g04 - modification time, 01-jan-2000 12:34:56
cm7n0g04 - modification time, 01-jan-1970 00:00:00
cm9n0g04 - modification time, 31-dec-1999 23:59:59
ct0n0g04 - no textual data
ct1n0g04 - with textual data
ctzn0g04 - with compressed textual data
cs3n2c16 - color, 13 significant bits
cs3n3p08 - paletted, 3 significant bits
cs5n2c08 - color, 5 significant bits
cs5n3p08 - paletted, 5 significant bits
cs8n2c08 - color, 8 significant bits (reference)
cs8n3p08 - paletted, 8 significant bits (reference)
cdsn2c08 - physical pixel dimensions, 8x8 square pixels
cdhn2c08 - physical pixel dimensions, 32x8 high pixels
cdfn2c08 - physical pixel dimensions, 8x32 flat pixels
cdun2c08 - physical pixel dimensions, 1000 pixels per 1 meter