Update: As noted in the comments, the presence of these images in the original Mac ROMs has been known for years, so this decoding project qualifies as a "rediscovery" rather than an original find.
The folks from NYC Resistor found an old Macintosh SE computer on the side of the road in Brooklyn, NY. The team grabbed the device and started to dig into the Macintosh's ROM. Using modern tools on the old code obtained from a ROM dump, the team pulled four images that were added to the ROM as an Easter egg. The images, available on NYC Resitor's website, are reportedly of the team that created the ROM and each one shows a different group of people.
Besides images, the NYC Resistor team also found a fifth surprise buried in the ROM, but they couldn't parse it out of the ROM at this time. Based on the strings in the ROM, the team guesses that it could be an audio file. You can read the details on how they tracked down these images in the ROM on NYC Resistor's website.