On a dark environment I used flashlight of my phone and took the photo with my camera.
It's also when I saw the shadow of my ponytail that I got the idea of the logo of my head with ponytail and that I used as a pendant necklace.

Hi Jesus,
I have to admit this has to be the first time I recall someone posting a hair pic in silhouette. Its a cool effect and interesting way to represent your hair. Looks like you nailed it so was this on the first take or did you have to take several shots until you got the one that looked best?Cheers.
Mârk aka Hairball
Hi Mark,
I did some shots and despite the camera have a stabilized sensor, it's not easy to avoid motion blur in these conditions: holding smartphone in one hand and camera on the other.
The photo was shoot here.
Wow Jesus, I had no idea how large that image was until you posted the link to that retaining wall. It literally looks like a mural on that
large wall.I never thought of doing such a pic which has to be a first of that type here.Cheers.
Mârk aka Hairball
Hi Jesus,
This is just so cool, and I’ve never tried it myself. I need to find a better way to take photos, though, other than the selfie mode of my phone. A photo like this needs someone else to take it for you, or some way to support either the camera or phone outdoors. I also need to practice bun styles, something that I’ve never tried. Always a ponytail for me when I need it confined.
David
You'll need a single point light to have a sharp shadow, a phone flashlight do the job and a camera tripod to hold the camera and avoid blur.