A method, performed by an image-processing device (120, 260), for detecting a reflection of an identified object in an image frame captured by a camera, the method comprising: - generating a three-dimensional model of a background scene of the image frame based on obtained three-dimensional information about the background scene; - defining the identified object in the image frame based on image information in the image frame; - defining a three-dimensional bounding box of the defined object in the three-dimensional model of the background scene; - defining surface elements of the three-dimensional bounding box, a respective surface element being defined by a centre coordinate in the three-dimensional model of the background scene and a colour value; - determining a three-dimensional coordinate of a surface in the three-dimensional model of the background scene which reflects light from a surface element of the three-dimensional bounding box of the object into the camera, wherein the determining is performed by tracing rays from the centre coordinate of the surface element of the three-dimensional bounding box of the object and based on a normal of the surface in the three-dimensional model of the background scene at said three-dimensional coordinate; - identifying a first pixel in the image frame which corresponds to the determined three-dimensional coordinate of the surface; - detecting the reflection of the object in the image frame when a mixing of a first colour value of the identified first pixel and the colour value of the surface element of the object and a ground truth colour value of the identified first pixel fulfils a mixing criteria; and - in response to detecting the reflection of the object applying a mask to a pixel area of the image frame, the pixel area comprising the identified first pixel. - generating a three-dimensional model of a background scene of the image frame based on obtained three-dimensional information about the background scene; - defining the identified object in the image frame based on image information in the image frame; - defining a three-dimensional bounding box of the defined object in the three-dimensional model of the background scene; - defining surface elements of the three-dimensional bounding box, a respective surface element being defined by a centre coordinate in the three-dimensional model of the background scene and a colour value; - determining a three-dimensional coordinate of a surface in the three-dimensional model of the background scene which reflects light from a surface element of the three-dimensional bounding box of the object into the camera, wherein the determining is performed by tracing rays from the centre coordinate of the surface element of the three-dimensional bounding box of the object and based on a normal of the surface in the three-dimensional model of the background scene at said three-dimensional coordinate; - identifying a first pixel in the image frame which corresponds to the determined three-dimensional coordinate of the surface; - detecting the reflection of the object in the image frame when a mixing of a first colour value of the identified first pixel and the colour value of the surface element of the object and a ground truth colour value of the identified first pixel fulfils a mixing criteria; and - in response to detecting the reflection of the object applying a mask to a pixel area of the image frame, the pixel area comprising the identified first pixel.