An option to remember which images have been compressed

[pshemek]

Such option could save TinyPNG hits. The information could be stored in a json file. (Like this Grunt task does.)

[artiswilliams]

Agreed. I used that grunt task previous to switching to all npm scripts. Would appreciate this option. Uses MD5 hash of the file compared against a json file of md5 hashes of previously compressed files.