So we've had a couple of reports of images not showing in Gmail, after some digging it turns out peopel are using pixel block.
https://chrome.google.com/webstore/detail/pixelblock/jmpmfcjnflbcoidlgapblgpgbilinlem?hl=en

It's blocking some images and not others, anyone know anything about the logic they're using? I've got a 300px image that's being blocked and an identicle 65px image that's not.