Neil (nknauth here in this forum) had this awesome idea to use my image importer to create custom covers for cartridges.
I myself wondered if one could use a cartridge cover other than a screenshot, but my best idea was “Probably at some point I should ask zep if he can enable using some other images. Maybe. Someday.” :)

But neil's idea is actually working. Needs a small amount of hacking though: simply loading an image, taking a screenshot, loading an another cartridge, and saving that cartridge by hand just produces a gray square on the cart instead of the image.

BUT using this code in the image loader works:

function _update()
if (btnp(4)) then
load(“road”)
end
if (btnp(5)) then
save(“road.png”)
end
end

function _draw()
cls()
sspr(0,0,127,127,0,0)
end

So the steps are:

1. Create an “image cartridge” with the code above, but replacing “road” for the target cartridge name.
2. Import the cover picture into this “image cartridge” by using the image importer from my previous post, or simply just drawing directly in Pico-8
3. Run the “image cartridge”
4. Press “z” to load the target cartridge.
5. Press F7 to take a screenshot
6. Press “X” to save the target cartridge.

Done! You have your own shiny custom cover Pico-8 cartridge! :)