das Standbild
statue
A sculpture that depicts a standing person or animal, usually life-size or larger.
Auf dem Marktplatz wurde ein Standbild des Stadtgründers errichtet.
A statue of the city's founder was erected in the marketplace.

statue / still image
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statue
A sculpture that depicts a standing person or animal, usually life-size or larger.
Auf dem Marktplatz wurde ein Standbild des Stadtgründers errichtet.
A statue of the city's founder was erected in the marketplace.

'Standbild' is composed of 'Stand' (from 'stehen', to stand) and 'Bild' (image/picture). So it is literally a 'standing image'. This basic idea helps you understand all the meanings: the standing sculpture, the still image from a film, and the person standing still.
Das Video hielt an und zeigte nur noch ein Standbild.
The video stopped and showed only a still image.
The context tells you which meaning is intended. If it is about art or a public square, a statue is meant. In the context of film, video, or cameras, it refers to a frozen image. If someone is talking about a person and their reaction, the person has frozen.
Vor dem Museum steht ein beeindruckendes Standbild aus Bronze.
In front of the museum stands an impressive bronze statue.
In connection with statues, typical verbs are 'errichten' (to erect), 'aufstellen' (to put up), and 'enthüllen' (to unveil). The material is also often mentioned, e.g. 'ein Standbild aus Bronze' (a bronze statue) or 'aus Marmor' (made of marble).
Die Stadt ließ ein Standbild zu Ehren der berühmten Wissenschaftlerin errichten.
The city had a statue erected in honor of the famous scientist.
In the meaning 'freeze-frame', 'Standbild' (still image) often occurs together with words like 'Video' (video), 'Film' (film), 'Kamera' (camera), or 'Aufnahme' (recording). It refers to the result when motion is stopped.
Die Polizei analysiert das Standbild der Überwachungskamera.
The police are analyzing the still image from the surveillance camera.
When a person is meant, the fixed expression 'zum Standbild erstarren' (to freeze like a statue) is almost always used. This expresses that someone suddenly becomes completely motionless out of fear, surprise, or amazement.
Als sie die Gestalt im Dunkeln sah, erstarrte sie zum Standbild.
When she saw the figure in the dark, she froze like a statue.
monument / landmark
'Denkmal' and 'Standbild' can both refer to a statue in a public space. 'Denkmal' mainly says that something is meant to commemorate a person or an event. 'Standbild' describes the form more strongly: it is a sculpture of a standing person or animal. A 'Standbild' can be a 'Denkmal', but it is not always called that. The risk of confusion comes from the fact that many monuments are designed as statues. If remembrance is important, use 'Denkmal'. If you are describing the type of statue, 'Standbild' fits.

Vor dem Theater steht ein Standbild eines berühmten Schauspielers.
In front of the theater stands a statue of a famous actor.
Wir besuchen das Denkmal, weil es an ein wichtiges Ereignis erinnert.
We visit the monument because it commemorates an important event.