FaceMash is an old web application that allowed people to compare two facial images side-by-side and choose who is more attractive. Here is a brief overview:

Crowdsourced Attractiveness Rating
The primary function of FaceMash was to enable visitors to repeatedly pick the photo they considered more good-looking out of a randomly presented pair of facial images. Over many comparisons, a consensus attractiveness score emerged.

Source Photos
The photos used on FaceMash were sourced from university student ID card images from Harvard at the time without explicit permission. This controversial usage sparked debates about privacy.

Basic Image Display
On each page, the site simply displayed two images side-by-side. Only the most basic photo functionality was implemented without additional editing or analysis capabilities.

Ranking Mechanism
As more choices were made between pairs of photos, FaceMash calculated and assigned each image an attractiveness ranking score. Standings of the top best and worst rated faces were displayed.

Viral Spread
In its brief active period at Harvard, FaceMash gained viral popularity on campus. Students were intrigued to humorously interact and discuss with the attractiveness rating comparisons, although controversy quickly ensued.

In summary, FaceMash exemplified common early internet applications - simple, viral idea for entertainment but with thorny issues around permissions. Its founder Mark Zuckerberg later apologized for the app. But it laid the foundation that led him soon after to build Facebook, with more responsible principles applied to user generated content.