encode image to secret html-file
checksum=eimg2shtml(imgFilename,htmlFilename,key[,title[,legend]])
imgFilename :
string of image-filename (PNG- or JPEG-file)
htmlFilename :
string of html-filename
key :
vector of unsigned char
or string
title :
title of image
legend :
legend under password entry
checksum :
checksum of cipher