ISO was originally made as a custom typeface to use in EXIF.co, a new tool for photographers to protect their work online. It was inspired by old cameras, specifically Leicas. They have this really warm, slightly goofy, and tactile engraved text all over. We were also looking at film negatives for the EXIF.co brand, so we started to push this into a more mechanical sans.
The choice to go with a monospace was partly influenced by this, but it was also practical. We needed to calculate the length of user names in the watermark. Having a set width for all glyphs makes that much simpler.
We paired ISO with Calibre (Black)for the headers to give it a nice powerful contrast.