From J Hochenbaum:
Use this website for all images:
"All sounds good dude. One quick nerd thing, I think we should go back and run all of our original images through http://www.jpegmini.com/ for compression. The images we upload are super quality JPG, and indeed, SquareSpace reduces their image dimensions to a number of sizes automagically when uploading so they are reduced in dimensions and filesize to their actual viewing sizes on different devices (this is good!). However, JPGMinis compression is a bit better-- i redownloaded one of the fullscreen images from the website and it reduced its size in half without any image loss. So I think we we replace all our media with pre-compressed JPGs, squarespace will still resize em, and we should gain the benefit on smaller file sizes = faster load times."