Camera tampering detection

1. A method for identifying possible tampering of a camera view, said method comprising:

receiving an image for analysis from an image sequence,

converting the received image into an edge image,

generating a similarity value indicating a level of similarity between said edge image and a reference edge image,

indicating possible tampering of the camera view if the similarity value is within a specified tampering range,

updating the reference edge image by combining a recently analyzed edge image with the reference edge image in case of each one of a predetermined number of consecutively analyzed images does not result in an indication of possible tampering,

counting the number of consecutively analyzed images resulting in an indication of possible tampering, and

generating an alarm signal in case of each one of a predetermined number of consecutively analyzed images does result in an indication of possible tampering, wherein said predetermined number is larger than one.

2. Method according to claim 1 , further comprising the act of decreasing the resolution of the image to be converted into an edge image.

3. Method according to claim 2 , further comprising selecting a new image for analysis only after that at least one consecutive image of the image sequence has not been selected for analyzing.

4. Method according to claim 1 , further comprising counting by means of a counter n pt in response to said indicating possible tampering of the camera view.

5. Method according to claim 4 , further comprising generating an alarm signal if the counter n pt has reached a predetermined alarm limit.

6. Method according to claim 4 , further comprising counting by means of a counter n nt in response to said similarity value not being within said tampering range and resetting the counter n nt if the currently analyzed image resulted in the counter n pt counting and the previously analyzed image resulted in the counter n pt counting.

7. Method according to claim 6 , further comprising resetting the counter n nt if the currently analyzed image resulted in the counter n pt counting and the previously analyzed image resulted in the counter n nt counting.

8. Method according to claim 6 , wherein said updating of the reference edge image is performed if the counter n nt has counted past a predetermined update limit.

9. Method according to claim 1 , wherein the updating of the reference edge image by combining a recently analyzed edge image with the reference edge image comprises combining the recently analyzed edge image multiplied with a first factor to the reference edge image multiplied with a second factor.

10. Method according to claim 9 , wherein the first factor is of a value less than one and wherein the second factor is of a value corresponding to one minus the first factor.

11. Method according to claim 1 , wherein only one edge image and one reference edge image is stored in memory for use by the method at any given time.

12. An apparatus for identifying possible camera tampering, said apparatus comprising:

an edge image generator arranged to receive an image for analysis from an image sequence and arranged to convert a received image into an edge image,

a correlation evaluator arranged to generate a similarity value indicating a level of similarity between an edge image and a reference edge image and to indicate possible tampering of the camera view if the similarity value is within a specified tampering range,

a reference edge image updater arranged to update the reference edge image by combining a recently analyzed edge image with the reference edge image in case of each one of a predetermined number of consecutively analyzed images do not result in an indication of possible tampering,

a counter arranged to count the number of consecutively analyzed images resulting in an indication of possible tampering, and

an alarm signal generator arranged to generate an alarm signal in case of each one of a predetermined number of consecutively analyzed images do result in an indication of possible tampering, wherein said predetermined number is larger than one.

13. Apparatus according to claim 12 , further comprising a scaling unit arranged to decrease the resolution of the image that is to be converted into an edge image.

14. Apparatus according to claim 12 , further comprising a counter n pt arranged to count indications of possible camera tampering.

15. Apparatus according to claim 14 , further comprising an alarm generator arranged to generate an alarm signal if the counter n pt has reached a predetermined alarm limit.

16. Apparatus according to claim 14 , further comprising a counter n nt arranged to count analyzed images determined not to be within said tampering range, wherein the correlation evaluator additionally is arranged to reset the counter n pt if the currently analyzed image resulted in the counter not counting and the previously analyzed image resulted in the counter n pt counting.

17. Apparatus according to claim 16 , wherein the correlation evaluator additionally is arranged to reset the counter n nt if the currently analyzed image resulted in the counter n pt counting and the previously analyzed image resulted in the counter n nt counting.

18. Apparatus according to claim 16 , wherein the reference edge image updater is arranged to perform said updating of the reference edge image if the counter n nt has counted past a predetermined update limit.

19. Apparatus according to claim 12 , wherein the reference edge image updater is arranged to combine a recently analyzed edge image with the reference edge image by combining the recently analyzed edge image multiplied with a first factor to the reference edge image multiplied with a second factor.

20. Apparatus according to claim 19 , wherein the first factor is of a value less than one and wherein the second factor is of a value corresponding to one minus the first factor.

21. A monitoring camera including the apparatus according to claim 12 .

22. A monitoring camera performing the method according claim 1 .

23. A video server including the apparatus according to claim 12 .

24. A video server performing the method according to claim 1 .