What photo ID to use for the Deutschland Ticket?

Deutshland-dicket terms of carriage § 2 (6) 5 says:

Zur Legitimation ist ein amtliches Lichtbilddokument mitzuführen und bei Kontrollen vorzuzeigen.

Amtlich means issued by a government agency. Lichtbilddokument is a document containing a photograph. Examples are:

• driver’s license (motor vehicle)
• electronic health insurance card (at least if issued by Germany’s statutory health insurance)
• firearms license
• mariner credential
• military ID
• national ID (including preliminary IDs)
• official ID card (e. g. of the police, customs, THW)
• passport (including diplomatic and emergency passports among others)
• radio operator’s license
• refugee travel document
• residence permit
• severely disabled person ID (at least if issued by the German Versorgungsamt)
• stateless person travel document
• student ID (from certain countries/universities)
• train driver’s license

Note, the terms of carriage do not say whether the presented document has to be still valid, neither is it required the government (agency) still exists (consider the GDR or FSU).

You see you have a rich trove of documents to choose from. In reality, however, I am afraid showing your, say, Japanese Aeronautical Radio Operator license will not be accepted. The ticket inspector will have a hard time to distinguish between genuine and counterfeit documents.

You will have the least troubles with a German national ID or a German passport. That is for sure. In border regions standard documents of the neighboring countries will be fairly well accepted, too. Everything else is already risky. You have a passport from Saint Lucia? “Well, sorrrry, but I have never heard of ‘Saint Lucia’. Sounds like a made-up country.”

Could a photocopy of the passport, or a picture of it in my phone be sufficient?

No, the terms of carriage indicate you have to carry the document on you. A copy is a copy, not the document itself.

Given that I am not a German or EU citizen, what sort of ID should I carry with me? […] The only other photo IDs that I have are my own country's identity card and driving license […]

It is ridiculous, but carry them all. Passport, ID, driver’s license, at times Germans can be a pain in the butt.

Are there any other options which I am missing?

No, except, of course, using a different ticket. In some localities you will find, for instance, a regionally limited monthly pass ≤ €49 that is not tied to a specific person. I presume your internship will not require traveling the whole nation anyways, so check your options.

The €49 ticket has been a political project, introduced to allow residents to stop driving individual cars. The purpose is (a) to reduce CO2 emissions and (b) to compensate for the price increase of gasoline and diesel because of the Russian attack on Ukraine. Last year, there was an €9 ticket for a couple of months, charging €49 now is still subsidized but more sustainable for the public budget.

The ticket is valid for local transport nationwide and it can be sold by different transport companies, with slightly different rules from state to state. Yet companies in any state should accept tickets issued in any other state. It might be a good idea to ask your local public transport provider about their policy.

Beyond that, there is the Deutsche Bahn, the national rail company. The €49 ticket is valid in their local trains, but not in their long distance trains.

Here, the Bahn website talks about ID documents in conjunction with online tickets. They accept identity cards from EU countries, passports from other countries, and some special cases.

Here, the Bahn website talks about ID documents and list European, Swiss, and Norwegian ID cards. This strongly implies that they read 'European' as EU, whatever the geographical realities.

Here, the Bahn website mentions the physical BC100 card on a page directly linked from the €49 ticket, which looks like nonsense.

My conclusions are:

1. The Bahn is still confused how to handle the recent nationwide ticket.
2. They mean "EU/EEA identity card or international passport", even if it might be possible to talk an individual conductor into accounting other ID cards.

The expression "amtlicher Lichtbildausweis" (official picture id) is unambiguous without further explanation.

For all practical purposes, you need either:

• a German national id card
• a national id card from an EU/EEA state
• or a passport

The same requirement also applies to other ticket types, it is not new for the Deutschland-Ticket that you may have to show an id during ticket inspection, and DB is known to be very strict in their interpretation. There have been several cases reported in media, where for example non EU/EEA citizens have been thrown off the train because they can only show their national id card. Driver's licences are generally not accepted as id in Germany.