Mine

import os, sys

for root, dirs, files in os.walk(".") :
    for name in files :
        if name.lower()[-4:] != ".png" :
            continue
            
        if name == ".temp.png" :
            os.system("del .temp.png")
            continue
            
        filename = root + "\\" + name
        
        os.system("copy /b \"%s\" .temp.png" % filename)
        os.system("pngcrush -q -force -rem gAMA -rem cHRM -rem iCCP -rem sRGB -rem tEXt -rem zTXt -ztxt b \"Author\" \"Tone Marie Berg\" .temp.png \"%s\"" % filename)
        os.system("del .temp.png")
        
        for i in xrange(6) :
            os.system("pngout /y /f%d /kzTXt \"%s\"" % (i, filename))