The COVID-19 pandemic has forced many higher education institutions to offer their courses online, which is quite challenging when implementing laboratory sessions. Here we describe a web-based teaching resource consisting of a metallographic atlas with more than 200 micrographs corresponding to pure metals, binary alloys, steels, cast irons, and light alloys. The atlas is designed for majors and graduate level students in materials science disciplines, and it focuses on the interpretation of optical micrographs. The web page metrics, the impact on academic scores, and the results of an anonymous and voluntary survey indicate a very positive response to this online teaching resource material.