If you will simply go read the requirements on the Consulate/Embassy pages about passports, you'll know what's required.
A photo shop here (one typically will have a sign in the window mentioning passport photos) will ask you what you want, country
involved (e.g., some countries use a different size for passport photos), etc. and they'll know the requirements regarding size,
background, glasses on or off, etc.
If you simply google "Chiang Mai Passport Photos", you'll see several places in the area.