This is actually codified for passports
https://en.wikipedia.org/wiki/Machine-readable_passport#Name...
https://en.wikipedia.org/wiki/Machine-readable_passport#Name...
Take a look at the spec if you are interested: https://www.icao.int/publications/documents/9303_p3_cons_en.... The transliteration tables start on page 24 and are scattered throughout the document.
Newer versions of the transliteration encourage stripping diacretics, so that would be HAMALAINEN. Much more readable to native speakers, but obviously loses information.
I wouldn't recommend it as there are official tranformations from the countries which uses diacretics and they most times are not to strip them. It's kinda another case of people forcing stuff onto other cultures. And if you do bussiness in some of the countries in some industries you might even get into legal trouble if you apply that.
> Section 6 of the 9303 part 3 document specifies transliteration of letters outside the A–Z range. It recommends that diacritical marks on Latin letters A-Z are simply omitted (ç → C, ð → D, ê → E, ñ → N etc.), but it allows the following transliterations: [...]
You said
> you might even get into legal trouble if you apply that.
We're talking about passports, this seems not relevant. For passport-related use such as travel, you use the form of the name written on the passport, exactly as-is.
its the only requirement because
1. it's only meant for OCR
2. it's clear that it won't be used by only OCR but at least also human interacting with the system, potentially phone calls passing this information by voice, and anyone who can't pronounce the original spelling. For fairness if you e.g. didn't sing at all in your life are somewhat tone deaf and now are expected to pronounce a asian you probably have to spend days or more until you can do so (just as a extreme example).