I implemented what I was looking for!
I started connecting various pieces of information I found on this forum, the wiki, and GitHub.
It took some time to JB and get wifi SSH access, then I wrote a few short scripts to get the behavior I was looking for, and I used FBInk to show the images.
NiLuJe's FBInk is the key element to make it work fine, as it allows to show almost any image I drop in the Kindle's storage without having to preprocess it. Thank you NiLuJe!!!
I'm sharing all the details in this GitHub repo:
https://github.com/aesuli/Kindle-Photo-Frame