1. A method to monitor an area ( 18 ) wherein a camera ( 11 ) captures at least one image of the area ( 18 ), and the captured at least one image of the area ( 18 ) is compared with a reference image assigned to the area ( 18 ), wherein the comparison is carried out on the basis of spatial gradients that are identified in the captured at least one image of the area ( 18 ), wherein the method further comprises determining a normalized cross-correlation gradient between spatial gradients in the reference image and the spatial gradients in the captured at least one image of the area ( 18 ), and wherein the comparison includes detecting edges of objects based on the spatial gradients in the captured at least one image of the area ( 18 ).