How can I extend my tourist visa in Bangkok, and what are the requirements for the application?

About the photo part, if you can print it out on photo-type paper, it MIGHT work. But I doubt it could work if you print on standard paper. There are photo and copy shops on the floor 1 level lower at Cheangwattana (B building) if you need to get your photo done.

You will be applying for a 60 day extension of stay based on unable to travel due to COVID-19. You can apply this NO SOONER THEN 3 business days before your current stamp expires. You will need the following:

1. Your passport and:

a. a copy of your data ("picture") page

b. a copy of your most recent visa (if you have one)

c. a copy of your most recent stamp

d. a copy of your departure card

2. A TM30, filed in the immigration office.

3. The forms. FOR BANGKOK IMMIGRATION, you can find it in the files section.

4. 2x passport pictures

5. 1,900 THB.

>Do I need to book a plane ticket at the end of September to prove them I'll get out of the country by the end of the extension?

Not for Bangkok immigration.

>; is it enough if it's printed or should I go have my photo taken somewhere (where?

I suppose you can print out the photo itself, as long as it meets the criteria. But I recommend getting them done professionally.