As the object is moved from infinity towards the pole of a concave mirror, the image formed starts shifting from the focus of the mirror towards infinity.
When the object is at infinity, the image is formed at the focus or in the focal plane.
As the object is shifted, the image is formed between the focus and the centre of curvature, then at the centre of curvature, then beyond the centre of curvature, then at infinity and finally the image is formed behind the mirror.