Astro Mosaic would not be possible without Aladin Sky Atlas (http://aladin.u-strasbg.fr/aladin.gml) and Aladin Lite (https://aladin.u-strasbg.fr/AladinLite/doc/). Aladin Sky Atlas is a great interactive map created from digitized astronomical images. It is simply amazing that such a great resource is available. And it is totally free!
Aladin Lite provides HTML5 and programmable Javascript API interface to Aladin Sky Atlas. It makes it very easy to integrate into a web page. There are great examples and documentation to get started very quickly.
For displaying images Aladin Lite uses preprocessed data from HiPS (http://aladin.u-strasbg.fr/hips/). HiPS (Hierarchical Progressive Surveys) is the hierarchical tiling mechanism which allows users to access, visualize and browse seamlessly image, catalogue and cube data. There are 250TB of data available from different HiPS surveys.