क्या आपने उस लड़की का चेहरा तस्वीर में देखा?

At the start of a sentence, क्या often marks a yes/no question.

So:

• क्या आपने उस लड़की का चेहरा तस्वीर में देखा? = Did you see that girl's face in the picture?

It does not mean what here.
When क्या means what, it usually appears where the thing being asked about would normally go, not just as a question marker at the front.

आपने = आप + ने

• आप = you (formal/polite)
• ने is a grammatical marker used very often with perfective transitive verbs in Hindi

Since देखा is a perfective form of a transitive verb (to see), Hindi normally uses ने with the subject:

• आपने देखा = you saw / you have seen

This is a very common pattern in Hindi.

Yes. आप is the polite/formal word for you.

So this sentence sounds polite or respectful.
If you were talking to a friend, you might use तुम instead:

• क्या तुमने उस लड़की का चेहरा तस्वीर में देखा?

The meaning stays basically the same, but the level of formality changes.

उस is the oblique form of वह.

Hindi uses oblique forms before postpositions, and here the phrase is part of a genitive construction with का:

• वह = that / he / she in a basic form
• उस = oblique form used in structures like उस लड़की का...

So:

• वह लड़की = that girl
• उस लड़की का चेहरा = that girl's face

Because of the का construction, उस is needed here.

It literally means:

• उस = that
• लड़की = girl
• का = of
• चेहरा = face

So the structure is literally:

• the face of that girl

In natural English, this becomes:

• that girl's face

This is a very common question.

In a का / की / के possessive phrase, the possessive marker agrees with the thing possessed, not with the possessor.

Here:

• possessor = उस लड़की = that girl
• thing possessed = चेहरा = face

Since चेहरा is masculine singular, the correct form is का:

• उस लड़की का चेहरा

Compare:

• उस लड़की की किताब = that girl's book
  because किताब is feminine

So का is agreeing with चेहरा, not with लड़की.

तस्वीर में means in the picture or in the photo.

• तस्वीर = picture, image, photo
• में = in

So the sentence is asking whether you saw the girl's face within the picture/photo.

Hindi word order is more flexible than English, though the verb often comes at the end.

So:

• क्या आपने उस लड़की का चेहरा तस्वीर में देखा?

is natural, but you could also say:

• क्या आपने तस्वीर में उस लड़की का चेहरा देखा?

Both are fine and mean essentially the same thing:
Did you see that girl's face in the picture?

The placement can shift for emphasis or style, but देखा usually stays near the end.

Because in this kind of sentence, the verb often agrees with the direct object if the subject has ने and the object is not marked with को.

Here:

• subject = आपने
• object = उस लड़की का चेहरा
• head noun of the object = चेहरा = masculine singular

So the verb appears as देखा to match चेहरा.

If the object were feminine singular, you would often get देखी instead.

Because चेहरा is the direct object, and in Hindi, direct objects are often left unmarked when they are inanimate or not taking को for emphasis/specificity.

Here, चेहरा is an inanimate noun, so को is not necessary.

You will often see को with animate or highly specific objects, especially people:

• क्या आपने उस लड़की को देखा? = Did you see that girl?

But in this sentence, you are seeing the face, not the girl as the direct object.

By itself, देखा is a perfective form, and depending on context it can correspond to English:

• saw
• have seen

So this sentence could be understood as either:

• Did you see that girl's face in the picture?
• Have you seen that girl's face in the picture?

Usually the surrounding context tells you which English translation sounds best.

Yes, sometimes. Hindi can form yes/no questions through intonation alone, especially in speech.

For example:

• आपने उस लड़की का चेहरा तस्वीर में देखा?

can also sound like a question if spoken with questioning intonation.

But starting with क्या is very common and clear, especially for learners and in standard written Hindi.

It can mean both picture and photo, depending on context.

So तस्वीर में can mean:

• in the picture
• in the photo

If someone wants to be very specific about a photograph, they might also use words like फोटो or फ़ोटो, but तस्वीर is very common and natural.

A rough breakdown is:

• क्या = question marker
• आपने = you + ने
• उस लड़की का चेहरा = that girl's face
• तस्वीर में = in the picture
• देखा = saw

So very literally:

• Question-marker you that girl's face picture in saw?

Natural English rearranges this into:

• Did you see that girl's face in the picture?

This is a good example of Hindi's usual tendency to put the verb at the end.