$ file 1x1.png 
1x1.png: PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced
$ perl -MFile::LibMagic -E'say File::LibMagic->new->describe_filename("1x1.png")'
PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced