1. Convert an image into ascii, e.g. using an online generator.
2. Split the ascii into strings that are no more than 4096 characters (pinescript limit).
3. Stack them together as cells on a table (as shown in the script).
I use code generation for step 2, by splitting the ascii file into chunks, then joining each line with a plus sign to make a large string concatenation statement, which I manually copy/paste into pine. Ideally, you could make this whole script into a template with a couple parameters.
Unfortunately, Pinescript doesn't use a monospaced font, so there will be some distortion. Feature request!
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.