How to use:

(optional) edit the code and choose your transparent color (default 0);
go to GFX editor, select the first tile marked with 'x'
drag and drop your PNG file;
you should see your image in the spritesheet;
RUN the cart
you see your image and how many CHARS the string will be long (if higher than 10k better optimise it further, e.g. kill stray pixels);
if the char count satisfies your expectations, press Ctrl+C to copy the image data (a string) in the clipboard;

Use it in your projectgame cart:

use Ctrl+P to enter Puny font mode (to respect pasted binary data)
just paste the copied string in your code like scr='(paste here)'
and print your string on screen: ?scr,0,0
(you may need to use a cls(n) with the same colour code as the transparent one declared when converting)

Comic example (3 full screens)
A -not so well optimised- example of a comic:

The comic example cart is here
Taking advantage of P8scii
Wide,Tall, Striped and Pinball modes
See comment below
(More to mention... using smaller blocks as sprites, transparency, etc...)