Monthly growth pictures confusion

Okay mommies, I'm taking monthly pictures of my little man, my question and confusion is, are they technically taken on the 19th of every month (he was born 9/19) or every 4th Monday (the 19th was a monday)? For example this past Monday was 8 weeks, however the 19th isn't until this Saturday so not sure which one is technically correct.

Hubby says the 19th of every month because we celebrate our birthdays on the day we were born, not going by the same day of the week to celebrate our birthday

I see other mommies I know going by the day of the week though.