Pocholo, OK
My method, (I hope Google will translate correctly ..) is to look in the dark (look without looking), let my eyes wander in the blur and suddenly the details of the object become clearer.

Fascinating thread. I've been trying to see these without success Asked a friend for help with Nidhogg's tee_hee.jpg and he saw the teapot. Going to keep trying!

Don't try too hard, just let your eyes go. Or ask your friend if you can switch eyeballs for a minute?

Now I'm happier about one or two things. First I tried Blender but my brain exploded and trickled on floor after 5 minutes of looking that mess of an interface. It has more buttons, switches, levers, meters and options than anything I've ever seen doublevisioned.
Then I remembered using Art of Illusion and Wings 3D about 20 years ago.
Art of Illusion was easy to install, 5 minutes and I had my first basic 3D model done yeehaa!
It's lot easier to make a depth map from 3D than 2D. Need still improve on the rendering settings for stereographs,
because it's easy to lose parts if the depth map is too dark or contrast too high.

Wow! That was amazing!
I had never experienced anything like that before!
After starting reading this thread from page 7 (post #63) and reading it backwards, I simply failed at every attempt.

I tried every image. Several minutes fixing each image in every way that was suggested during the reading. I failed at every attempt; at every one that came up from post #63 to #1.

It seems that like Wallace, OMG, and Pat I could not see the expected.
My eyes were already tired, watering, and after reading the post where Steve Reid comments that some people just can't see them (post #19) I was about to throw in the towel.

I had already opened Nidhogg's image (the one with texts) in the gimp before; unsuccessfully, I couldn't even see it after trying to apply his solution: "Duplicate layer, set the upper layer to difference and start moving it horizontally in 1px steps. At some point (depends on the used settings) it will be revealed."

But I tried again with the image from post #42.
Again several minutes fixing the image of all kinds. No result.

Then as if by magic, finally a crystal clear 3D image appeared in front of me! It looked like a hologram. I was amazed and after a few seconds I stretched my hand trying to feel the image hovering in the air in front of me, but this made me lose sight of it, leaving only the flat, coded image on the pc screen.

Wow... I had no idea how I got that. I tried again and again I had difficulty for several minutes, but I managed for the second time to make the image project a few centimeters from my face, suspended in the air, clear and so real. I stayed several seconds contemplating it, I could have total control of what I was seeing, of the pc screen in the background, of the details of the image, it was fantastic!

I never imagined that this was the vision that people had of these kinds of stereographs. I thought the image would reveal itself in the same plane as the original image, in 2d, like the one shown in post #58, but never suspended in front of me like a hologram.

Nidhogg thanks for that beautiful image!