Trag korišćenja je na slici.

Because trag is followed by a noun in the genitive case.

The basic noun is korišćenje = use / using.
Its genitive singular form is korišćenja.

So:

• korišćenje = nominative
• korišćenja = genitive

This pattern is very common in Serbian: noun + genitive to mean a sign/trace/result of something.

For example:

• trag dima = trace of smoke
• miris kafe = smell of coffee
• znak umora = sign of tiredness

So trag korišćenja literally means trace/sign of use.

Korišćenje is a verbal noun. It comes from the verb koristiti = to use.

So:

• koristiti = to use
• korišćenje = use, usage, using

English also does something similar with words like using or usage, but in Serbian these forms are very common and fully behave like nouns. That means korišćenje can take case endings, which is why you get korišćenja here.

Because Serbian normally says na slici for in the picture / in the photo / in the image.

This is just the usual idiomatic choice:

• na slici = in the picture
• na fotografiji = in the photograph

Using u slici would usually sound wrong here. It can mean something more like inside the image in a literal sense, or appear in other expressions such as biti u slici = to be informed / to be up to date.

So for visual content shown by a picture, na slici is the natural phrase.

Because after na with the meaning of location, Serbian uses the locative case.

The noun slika changes like this:

• slika = nominative singular
• slici = locative singular

So:

• na slici = on/in the picture

This kind of change is normal in Serbian declension. The consonant also changes a bit:

• k → c before i

That is why slika becomes slici, not slikai or something similar.

Je is the 3rd person singular of biti = to be.

So the sentence structure is basically:

• Trag korišćenja = the trace/sign of use
• je = is
• na slici = in the picture

So literally: The sign of use is in the picture.

In Serbian, je here is an unstressed clitic, so it usually appears in second position in the sentence or clause.

Yes. Serbian word order is more flexible than English word order.

You can say:

• Trag korišćenja je na slici.
• Na slici je trag korišćenja.

Both are correct.

The difference is mainly focus:

• Trag korišćenja je na slici. puts a bit more focus on the sign of use
• Na slici je trag korišćenja. puts a bit more focus on where it can be seen

Because je is a clitic, it still tends to stay in second position.

Because Serbian has no articles.

English distinguishes:

• a picture
• the picture

Serbian usually does not mark that difference with a separate word. Context tells you whether something is definite or indefinite.

So slika can mean:

• a picture
• the picture

depending on context.

If Serbian speakers want to be more specific, they can use words like:

• ova slika = this picture
• ta slika = that picture

But in a normal sentence like this, no article is needed.

Serbian often uses singular in expressions like this even when English might prefer a plural idea such as signs of use or wear marks.

So trag korišćenja can work as a general statement meaning that some visible evidence of use is present.

If you want to emphasize several marks, you can use the plural:

• Tragovi korišćenja su na slici. = The signs of use are in the picture.
• Tragovi korišćenja vide se na slici. = Signs of use can be seen in the picture.

So the singular here is not strange; it is just a natural Serbian way to phrase it.

A rough English-friendly approximation is:

ko-REE-shche-nya

A few details:

• š sounds like sh
• ć is a soft sound, something like a very мягкий ch/t sound; learners often approximate šć as shch
• nj sounds like the ny in canyon or the Spanish ñ

So korišćenja has roughly four syllables:

ko-ri-šće-nja

You do not need a perfect English equivalent, because some Serbian sounds do not match English exactly, but that approximation is good enough to start.

Yes, very much so.

In product descriptions, sales posts, and online listings, Serbian often uses short practical phrases like this to mean that any wear or damage can be seen in the photo.

So Trag korišćenja je na slici. sounds like the kind of sentence you might see when someone is selling a used item and wants to say that the mark of wear is visible in the picture.

In that kind of context, you may also see similar phrases such as:

• Oštećenje je na slici. = The damage is in the picture.
• Stanje je prikazano na slici. = The condition is shown in the picture.
• Sve se vidi na slici. = Everything can be seen in the picture.