[foton1981]

https://github.com/bslatkin/dpxdt

[heyalexej]

Here's a Video that explains how the Google Survey team uses perceptual visual diffs (dpxdt) in their deployments: https://www.youtube.com/watch?v=UMnZiTL0tUc

[wickedlogic]

It is an option, in fact there are a lot of open source options. The subscription model we offer is one way to gain the ability without having to worry about the complications of hosting it.