The photograph was taken from an altitude of about 60 miles with the 80mm lens from the window of Charlie Brown during rendezvous with Snoopy’s ascent stage before docking and transfer of the crew in the CSM and jettison of Snoopy’s ascent stage.
The red/blue diagonal line is the Command Module’s window. Unlike the subsequent Apollo 11 ascent stage (and all that followed it), which was left in lunar orbit to eventually crash into the lunar surface, Snoopy’s ascent stage was sent on a trajectory past the Moon into a heliocentric orbit. This was not tracked after 1969, and Snoopy’s location remained unknown until 2011, when a group of amateur astronomers based in the UK started a project to search for it. The Royal Astronomical Society announced a possible rediscovery of Snoopy in 2019, positing that asteroid “2018 AV2,” which is roughly the size of a school bus, is likely the capsule. The Apollo 10 LM Snoopy is the only once-manned spacecraft still in outer space without a crew.
From the mission transcript during the docking with Charlie Brown:
106:19:13 Engle (Mission control):
Snoopy, this is Houston. How do you read me?
106:19:15 Stafford (Snoopy):
So far it looks good.
106:19:19 Cernan (Snoopy):
Hey, Joe. We’re about ready to dock. Stand by.
106:19:22 Stafford (Snoopy):
Don’t call us. We’ll call you.
106:20:14 Stafford (Snoopy):
OK, John. You’re in to about 5 feet, babe. Looking beautiful. [...]
106:21:14 Cernan (Snoopy):
We got a capture, John. Fire when you’re ready. [...]
106:22:12 Stafford (Snoopy):
Hello, Houston. Snoopy and Charlie Brown are hugging each other.