A spatial relationship is determined between a first image of a first region of a physical space, and a second image of a second region of that space; and the first and second images are thereby stitched together into a composite image comprising first and second areas derived from the first and second images respectively. Further, there is detected an embedded signal having been embedded in light illuminating at least part of the first region of the physical space upon capture of the first image, the embedded signal conveying metadata relating to at least part of the physical space. An effect applied to at least part of the first area of the composite image based on the detected metadata; and also, based on the detected metadata and on the determined spatial relationship between the first and second images, the effect is applied to at least part of the second area of the composite image that extends beyond the first area.