Tôi nghe nói ảnh phong cảnh này rất sắc nét.

Because nghe nói is a very common Vietnamese expression for reporting something you have heard from other people.

• nghe = to hear
• nói = to say / speak

So literally it is something like hear said, but naturally it means:

• I heard that...
• I've heard that...
• People say that...

In this sentence, Tôi nghe nói introduces information that the speaker learned indirectly, not by personally checking it.

Usually, no explicit word is needed.

English often says:

• I heard that this landscape photo is very sharp.

Vietnamese can simply say:

• Tôi nghe nói ảnh phong cảnh này rất sắc nét.

Sometimes Vietnamese may include là or rằng in more formal or careful speech, but in everyday Vietnamese they are often omitted.

For example:

• Tôi nghe nói là ảnh phong cảnh này rất sắc nét.
• Tôi nghe nói rằng ảnh phong cảnh này rất sắc nét.

All of these are understandable, but the version without là/rằng is very natural.

This is a noun phrase where one noun modifies another.

• ảnh = photo, picture, image
• phong cảnh = scenery, landscape

So ảnh phong cảnh means:

• landscape photo
• photo of scenery
• landscape picture

Vietnamese often puts the main noun first and the describing noun after it, so:

• ảnh chân dung = portrait photo
• ảnh cưới = wedding photo
• ảnh phong cảnh = landscape photo

You do not need a separate word like of here.

Because Vietnamese demonstratives usually come after the noun phrase.

So:

• ảnh này = this photo
• người này = this person
• cuốn sách này = this book

In your sentence, này comes after the full noun phrase:

• ảnh phong cảnh này = this landscape photo

This is the normal Vietnamese pattern. English says this photo, but Vietnamese says something more like photo this.

Vietnamese often does not use a verb meaning to be when an adjective is the predicate.

So in English:

• This landscape photo is very sharp.

In Vietnamese:

• Ảnh phong cảnh này rất sắc nét.

Literally, it looks like:

• landscape-photo this very sharp

That is completely normal in Vietnamese.
When an adjective describes the subject directly, no is/are is needed.

Compare:

• Cô ấy đẹp. = She is beautiful.
• Trời nóng. = The weather is hot.
• Ảnh này sắc nét. = This photo is sharp.

Rất means very.

So:

• sắc nét = sharp / clear / crisp
• rất sắc nét = very sharp / very clear

It is an intensifier placed before the adjective.

Examples:

• rất đẹp = very beautiful
• rất tốt = very good
• rất rõ = very clear

If you remove rất, the sentence still works:

• Tôi nghe nói ảnh phong cảnh này sắc nét.

That just sounds a little less strong.

Sắc nét usually means something like:

• sharp
• clear
• crisp
• well-defined

It is especially common for:

• photos
• images
• screens
• printed text
• visual details

For a photo, rất sắc nét suggests the image quality is clear and detailed, not blurry.

Learners sometimes wonder whether sắc and nét should be understood separately, but in practice sắc nét works as a fixed expression meaning sharp/clear in detail.

Yes, ảnh is very common and natural.

It can mean:

• photo
• picture
• image

Depending on context.

If you want to be a little more specific, Vietnamese also sometimes uses measure words/classifiers such as:

• bức ảnh
• tấm ảnh

So you may also hear:

• Tôi nghe nói bức ảnh phong cảnh này rất sắc nét.
• Tôi nghe nói tấm ảnh phong cảnh này rất sắc nét.

These are also natural.
The original sentence without bức/tấm is still perfectly fine.

Tôi means I and is a neutral, polite first-person pronoun.

In many situations, Vietnamese can omit the subject if it is already clear from context. So if people already know you are talking about your own opinion/report, you might sometimes hear just:

• Nghe nói ảnh phong cảnh này rất sắc nét.

That sounds like:

• Heard that this landscape photo is very sharp.

But in a full standalone sentence, Tôi nghe nói... is clearer and more complete.

Yes.

• nghe = hear / listen
• nghe nói = hear that / hear people say / be told

Compare:

• Tôi nghe tiếng nhạc. = I hear music.
• Tôi nghe nói anh ấy sắp đi. = I heard that he is about to leave.

So in your sentence, nghe nói is not about physically hearing the photo. It means the speaker received information from other people.

Yes. The exact English wording can vary depending on context.

• ảnh can be photo, picture, or image
• phong cảnh can be scenery or landscape

So possible English equivalents include:

• this landscape photo
• this scenery photo
• this landscape picture
• this landscape image

Among these, this landscape photo is often the most natural.

Both are natural, but they feel slightly different.

• ảnh phong cảnh này = simple, common, everyday
• bức ảnh phong cảnh này = a bit fuller, sometimes slightly more careful or descriptive

Vietnamese often allows the classifier to be dropped in casual speech, especially when the meaning is already obvious.

So:

• ảnh này đẹp = natural
• bức ảnh này đẹp = also natural

Neither is wrong here.

A helpful breakdown is:

• Tôi = I
• nghe nói = heard that / have heard
• ảnh phong cảnh này = this landscape photo
• rất sắc nét = very sharp

So the sentence structure is:

[Speaker] + [reporting phrase] + [thing being talked about] + [description]

That is:

• Tôi
• nghe nói
• ảnh phong cảnh này
• rất sắc nét

This is a very normal Vietnamese pattern.

Yes, a few.

Common tricky words:

• tôi — the ôi sound may take practice
• ảnh — watch the tone; it is different from anh
• cảnh — also has a tone and final consonant that learners may miss
• sắc nét — both words have tones, and they should not be pronounced flat

A big learner issue is remembering that tones change meaning. For example, ảnh and anh are not the same word.

Even if your grammar is correct, incorrect tones can make the sentence harder to understand, so this sentence is a good one for slow tone practice.