Vem som än ser hennes leende säger att bilden känns varm och naturlig.

It is a fixed expression meaning whoever or no matter who.

So:

• vem = who
• som än adds the idea of it doesn’t matter who

So Vem som än ser hennes leende... means Whoever sees her smile... / No matter who sees her smile...

This structure is very common in Swedish:

• vad som än händer = whatever happens
• var du än bor = wherever you live
• när som helst is related in the sense of free choice, though built differently

No. Even though än often means than in comparisons, that is not what it means here.

In the pattern question word + som + än, it gives a free-choice meaning:

• vem som än = whoever
• vad som än = whatever
• var som än / var du än = wherever

So in this sentence, än is not comparative at all.

Because after a possessive word like min, din, hans, hennes, vår, deras, Swedish normally uses the noun in its basic form, not the definite form.

So:

• leende = smile
• leendet = the smile
• hennes leende = her smile

Even though her smile is definite in meaning, Swedish does not usually add the definite ending after a possessive.

Compare:

• boken = the book
• hennes bok = her book, not hennes boken

Because se usually takes a direct object when you mean see in the normal sense of visually perceiving something.

So:

• ser hennes leende = sees her smile

If you say se på, it is closer to look at.

Compare:

• Jag ser bilen. = I see the car.
• Jag ser på bilen. = I am looking at the car.

In your sentence, the idea is not really looking at her smile in an intentional way, but simply seeing it. So ser hennes leende is the natural choice.

Because bilden means the picture/image, so it refers to a specific picture that is already known from the context.

• en bild = a picture
• bilden = the picture

The sentence is talking about one particular image, not just any image in general.

Right — here känns is not literal.

The verb kännas often means:

• feel
• seem
• come across as

So bilden känns varm och naturlig means the picture gives that impression. It feels warm and natural to the viewer.

This is very natural Swedish. It does not mean the picture itself has emotions or physical sensation.

Compare:

• Rummet känns kallt. = The room feels cold.
• Texten känns äkta. = The text feels genuine.
• Bilden känns varm. = The picture feels warm.

Because känns is softer and more subjective.

• Bilden är varm och naturlig sounds more like a direct statement that the picture is warm and natural as a fact.
• Bilden känns varm och naturlig means that this is the impression people get from it.

In art, photography, design, and everyday description, Swedish very often uses kännas for this kind of subjective effect.

So känns fits the meaning very well.

Because these adjectives describe bilden, and bild is a common-gender noun (en bild).

Predicative adjectives agree with the noun:

• common gender singular: varm, naturlig
• neuter singular: varmt, naturligt
• plural: varma, naturliga

So:

• Bilden känns varm och naturlig.
• Fotot känns varmt och naturligt.
  because foto is neuter: ett foto

The sentence is built like this:

• Vem som än ser hennes leende = a clause acting as the subject
• säger = the main verb
• att bilden känns varm och naturlig = what they say

So the overall structure is:

[Whoever sees her smile] [says] [that the picture feels warm and natural].

A useful way to see it:

1. Vem som än ser hennes leende
   This whole part functions like the person who sees her smile / whoever sees her smile.

2. säger
   This is the finite verb of the main clause.

3. att bilden känns varm och naturlig
   This is a subordinate clause after att.

Inside the att-clause, the order is normal subordinate-clause order:

• bilden = subject
• känns = verb

No. Swedish verbs do not change for person or number in the present tense.

So:

• jag säger = I say
• du säger = you say
• han säger = he says
• de säger = they say

It is always säger.

So even though English distinguishes say and says, Swedish just uses säger for everyone.

Yes, absolutely. That would also be correct.

But the nuance is a little different:

• Alla som ser hennes leende... = All who see her smile...
• Vem som än ser hennes leende... = Whoever sees her smile... / No matter who sees her smile...

Vem som än sounds a bit more sweeping and emphatic. It stresses that the reaction is the same regardless of who the person is.

So both work, but vem som än gives a stronger no matter who feeling.