Valokuva todistaa, että auto oli paikalla.

Finnish does not have articles like English a/an and the.

So:

• valokuva can mean a photo or the photo
• auto can mean a car or the car

The exact meaning depends on context. In this sentence, the context tells us that we are talking about a specific photo and a specific car, so English often translates them with the.

Here todistaa is the 3rd person singular present tense form of the verb todistaa, meaning proves.

A useful thing to notice is that in many Finnish verbs, the basic dictionary form and the he/she/it form look the same. So:

• infinitive: todistaa = to prove
• 3rd person singular present: todistaa = he/she/it proves

In this sentence, valokuva is the subject, so todistaa means the photo proves.

In Finnish, a subordinate clause introduced by että is normally separated from the main clause with a comma.

So the sentence has two parts:

• main clause: Valokuva todistaa
• subordinate clause: että auto oli paikalla

This is very standard Finnish punctuation.

Että usually means that and introduces a clause explaining what is being said, known, proved, believed, etc.

Here:

• Valokuva todistaa = The photo proves
• että auto oli paikalla = that the car was there/present

So että connects the two parts, just like English that in The photo proves that...

Oli is the past tense of olla (to be).
On is the present tense.

So:

• auto on paikalla = the car is there / is present
• auto oli paikalla = the car was there / was present

The sentence is talking about a past situation that the photo proves, so oli is used.

Paikalla is the adessive case of paikka (place).

• paikka = place
• paikalla = at the place / on the spot / present there

In Finnish, expressions of location often use cases instead of separate words like at, in, or on.

With olla, paikalla is a very common expression meaning:

• to be present
• to be there
• to be on the scene / at the location

So auto oli paikalla means the car was physically present at that location.

Because auto is the subject of the subordinate clause:

• auto oli paikalla = the car was there

Subjects are usually in the nominative case, and auto is nominative singular.

Compare:

• auto oli paikalla = the car was there
• auton kuva = the car’s picture / picture of the car
• autolla = with the car / by car / on the car, depending on context

So here the plain nominative auto is exactly what we expect.

Yes, Finnish word order is fairly flexible, although the given sentence is the most neutral and natural order.

Neutral order:

• Valokuva todistaa, että auto oli paikalla.

You can change word order for emphasis, but the meaning or focus may shift. For example:

• Valokuva todistaa, että paikalla oli auto.
  This can emphasize that it was a car that was there.

• Että auto oli paikalla, sen valokuva todistaa.
  This is much more marked and less neutral.

So the original sentence is the best basic version for learners.

All of those are possible depending on context.

Paikalla often has the sense of:

• there
• present
• on the spot
• at the scene

So auto oli paikalla could be understood as:

• the car was there
• the car was present
• the car was at the location
• the car was on the scene

This word is often a bit more specific than just siellä (there), because it suggests being at the relevant place or scene.

Sometimes yes, but the nuance changes.

• auto oli siellä = the car was there
• auto oli paikalla = the car was there / present at the relevant location

Siellä is a general word for there.
Paikalla sounds more like at the place in question, on site, or present.

So in a sentence about evidence, a photo, or an event, paikalla often sounds more natural and more precise.

A few useful pronunciation points:

• että has a double t, so the t is held longer than in English-style pronunciation.
• paikalla has a double l, also pronounced longer.
• Finnish spelling is very regular: what you see is usually what you say.

Roughly:

• että ≈ ET-tä
• paikalla ≈ PAI-kal-la

Also remember:

• double consonants matter in Finnish
• double vowels matter too
• stress is normally on the first syllable of the word

So:

• VÁlo-kuva
• TÓdistaa
• Éttä
• Áuto
• Óli
• PÁikalla

Both are possible, but they are slightly different in scope.

• valokuva = photograph, photo
• kuva = picture, image, photo, illustration, depending on context

So valokuva is more specific: it clearly means an actual photograph.
If you said Kuva todistaa..., it could still work in many contexts, but it is a little broader and less precise.

In this sentence, valokuva makes it very clear that photographic evidence is being referred to.