I quite like this, it is very johnjohnston-ish. And I smiled knowing I was pinging your pi server.
You’d think and you did that the flickr API should do this, but its date stored seems to be unix time stamps. The lonly way I found to do via API ir here as a search, is to cycle through all years you’ve had flickr, and bracket for min-date taken and max date-taken. That seems like a lot to run through!
I am curious and also remembering I have an left over Pi from a closed project, and maybe I should see about doing what you are doing.
Happy days of photos during the holidays!