From photos. I can't do anything from memory which is one reason I'd never consider myself an artist. An artist can create. I can't do very much without some sort of reference.
Maybe the creating will come in time.
I said in my first post I'd been doing this for the past year. It's actually been a little longer because I did my first drawing around January or February of last year.
Let me tell you a story that might be of some help.
I played the trumpet since I was 9 years old all the way into adulthood. I can sight-read no problem -- the music goes from the sheet to the sound. But I was NEVER able to improvise. Even when I "improvised" it was technical -- a 3rd up, a 5th down, a riff heard on a recording. I was a good technical player but knew my limitations.
As an adult, I taught myself to play the flute. Once I learned overtones (accidentally) I found ALL I could do was riff. I was no Chris Wood, mind you (who is), but I could carry my own in a total improv. I rocked with some live band, making it up as I went. I found I had an instinctive feel for key and what works. I came closer to talented than with the trumpet. There is still a mechanical quality to my flute playing so I will never be great -- but at least I made to not 1/2 bad.
Interestingly I can NOT sight read with the flute AT ALL. My brain says "that is an A-flat quarter note and thus needs... When I want to know what a song sounds like and all I have is sheet musing I have to play it with the trumpet, then mentally transpose and free form it on the flute.
I have always found this an interesting personal insight into how the brain works and maybe a glimpse into the nature of talent.
Your artwork is very good. Many of us would give our left arm to even approach your level of artistry. That, my friend, is a gift from God given to very few. And did it occur to you your humor is where your art is?
Don't worry about needing a frame of reference. One day you will find your impromptu medium.