There are 2 repositories under screenshots-comparison topic.
Detailist is a simple tool that allows to take screenshots, compare screenshots using heatmap of differences and extract screenshots text (OCR).
Full page screenshot comparison (visual regression testing) can be used with Java, Groovy ...
Caravaggio is a simple visual regression testing plugin for Protractor.
Screenshot generation and comparison tool
[RESEARCH] Proof of concept minimum working setup of the Gemini, utility for regression testing of web pages using screenshots