Serienummeret står under bildet.

Because Norwegian usually adds the definite article to the end of the noun.

• et serienummer = a serial number
• serienummeret = the serial number

The ending -et is the definite singular ending for many neuter nouns, and serienummer is a neuter noun.

In Norwegian, the is often built into the noun itself instead of being a separate word in front of it.

So:

• serienummeret = the serial number
• bildet = the picture / the image

This is one of the biggest differences from English. English says the picture; Norwegian often says bildet.

For the same reason as serienummeret: bildet is the definite singular form.

• et bilde = a picture / an image
• bildet = the picture / the image

In this sentence, it refers to a specific picture, so the definite form is used: under bildet.

Yes, står literally means stands, but in Norwegian it is also very commonly used for the location of text, information, or objects.

So Serienummeret står under bildet literally looks like The serial number stands under the picture, but the natural meaning is more like:

• The serial number is under the picture
• The serial number appears under the picture
• The serial number is written below the picture

Norwegian often uses stå where English would use be, appear, or be written.

This is the normal word order for a simple Norwegian statement:

subject + verb + adverbial/place

So here:

• Serienummeret = subject
• står = verb
• under bildet = place expression

A very basic pattern in Norwegian is:

Something + is/stands + somewhere

You could also say Under bildet står serienummeret, but that sounds more like you are emphasizing the location. In both cases, Norwegian still keeps the verb in the second position.

Yes. Under means under / below.

In this sentence:

• under bildet = under the picture

Unlike languages such as German, modern Norwegian does not have a strong case system for ordinary nouns in this kind of phrase, so you do not need to change the noun because of under. You simply use the noun phrase after the preposition.

Yes. Norwegian very often writes compound nouns as one word.

So:

• serie
  • nummer → serienummer

This is completely normal in Norwegian. English sometimes writes similar expressions as two words, but Norwegian usually joins them together.

Both are neuter nouns.

Their indefinite forms use et:

• et serienummer
• et bilde

That is why their definite singular forms end in -et:

• serienummeret
• bildet

Yes. Bilde can mean several related things depending on context, such as:

• picture
• image
• photo
• sometimes illustration

So under bildet could mean under the picture, under the image, or below the photo, depending on what is being talked about.

Yes, potentially. The exact nuance depends on context.

Because of står, Norwegian often suggests that something is shown, printed, or written in that position. But in practical use, the sentence can simply tell you where to find it:

• The serial number is under the picture
• You can find the serial number below the image

So the sentence is often used as an instruction about where to look.