Is it possible to provide an image via stdin?

[uri]

I'd like to run something like:

pbpaste | gemini -p "do the thing I want with the image in stdin"

[Manamama]

Of course there is ;).

Assuming you mean an alias for xsel --clipboard --output, then:
xsel --clipboard --output > here_be_my_pretty_pic.jpg && gemini -p "Do admire my 'here_be_my_pretty_pic.jpg' ! Best way is via function call to read_file("here_be_my_pretty_pic.jpg"), oh yes, you can do so, Gemini AI..."
or such.
Depending on your clipboard content picture encoding, you may indeed even : xsel --clipboard --output | gemini -p "do the thing I want with the image hereinbelow: " , if not too long, tokens wise. I have not tried that yet, it should work in theory.

ver. 1.1: + the possibility of non-binary pipe entertained.