Отпечаток нужно выровнять.

Because нужно here is not the short adjective нужен meaning needed in a gendered way. It is the impersonal predicative word нужно, meaning it is necessary / one needs to.

So:

• Отпечаток нужен. = The print is needed.
• Отпечаток нужно выровнять. = The print needs to be aligned / It is necessary to align the print.

In your sentence, нужно introduces an action that has to be done, so it is followed by an infinitive: выровнять.

Because after нужно, Russian commonly uses the infinitive to say what action is necessary.

Pattern:

• нужно + infinitive

Examples:

• Нужно подождать. = It is necessary to wait.
• Нужно проверить документ. = The document needs to be checked.
• Отпечаток нужно выровнять. = The print needs to be aligned.

So выровнять is the action that must be done.

This is about aspect.

• выровнять = perfective
• выравнивать = imperfective

The perfective verb выровнять presents the action as a single completed result: to align / to make even / to straighten out completely.

With нужно, Russian often uses the perfective infinitive when the idea is this needs to be done and completed.

So:

• нужно выровнять = it needs to be aligned (focus on the finished result)
• нужно выравнивать would sound less natural here unless you mean an ongoing, repeated, or general process

Выровнять basically means to make even, level, straighten, or align, depending on context.

Possible translations include:

• align
• straighten
• level
• smooth out

The best English choice depends on what отпечаток refers to.

For example:

• in printing or design: align
• for a surface or shape: level / smooth out
• for something physically crooked: straighten

So the Russian verb is broader than any one single English translation.

Отпечаток can mean several related things, depending on context:

• print
• impression
• imprint
• mark
• sometimes fingerprint

Common examples:

• отпечаток пальца = fingerprint
• отпечаток на бумаге = print on paper
• отпечаток следа = impression/mark

So in this sentence, the exact meaning depends on the larger context. Grammatically, though, it is just the thing being acted on.

Отпечаток is in the accusative case, which for many masculine inanimate nouns looks exactly like the nominative.

Here is the key point:

• masculine inanimate nouns usually have
  • nominative singular: отпечаток
  • accusative singular: отпечаток

Since выровнять is a transitive verb, the object goes in the accusative:

• выровнять что? → отпечаток

So even though the form looks unchanged, its role in the sentence is the direct object.

Because this is an impersonal construction.

Russian often leaves out the person who has to do the action when that person is:

• obvious
• unimportant
• unknown
• deliberately unspecified

So Отпечаток нужно выровнять means something like:

• The print needs to be aligned
• It is necessary to align the print

This is very common in instructions, technical writing, manuals, and neutral statements.

If you wanted to name the person, you could:

• Мне нужно выровнять отпечаток. = I need to align the print.
• Нам нужно выровнять отпечаток. = We need to align the print.

Yes. Russian word order is flexible, and changing it can shift emphasis.

Your sentence:

• Отпечаток нужно выровнять.

This puts отпечаток first, which can make it the topic: as for the print, it needs to be aligned.

Other possible orders:

• Нужно выровнять отпечаток. = more neutral: It is necessary to align the print.
• Выровнять нужно отпечаток. = stronger emphasis on отпечаток as the thing that must be aligned

So the meaning stays similar, but the focus changes.

Yes, very often.

• Отпечаток нужно выровнять.
• Отпечаток надо выровнять.

Both can mean The print needs to be aligned.

In many situations, надо and нужно are close in meaning. Very roughly:

• надо can sound a bit more conversational
• нужно can sound a bit more neutral or formal

But in practice, both are common and natural.

Yes, but that is a different structure and slightly different in tone.

• Отпечаток нужно выровнять. = The print needs to be aligned / It is necessary to align the print.
• Отпечаток должен быть выровнен. = The print must be aligned / The print is supposed to be aligned.

The second version is more formal and more explicitly passive. It may sound like a requirement, rule, or specification.

Your original sentence is simpler and very natural, especially when talking about what needs to be done to something.