The image signature represents the image data contents of all frames as a 128-bit number that is reasonably sure to be unique. This is implemented using the RSA MD5 message digest algorithm.
No PropertyChanged notify is sent when this property becomes dirty. Instead track the ImageChanged event to see when you need to get a new CurrentSignature.
If image data has changed from its last access, getting the CurrentSignature is a fairly expensive computation, requiring the traversal of all pixels in all frames.
If you are only interested in whether image data has changed or not from some past time, the AllFramesUpdateCount property is a much faster way of making this check. The advantage of using CurrentSignature is that it can be saved after the application closes and it will be unchanged if identical data is written to an image (whereas AllFramesUpdateCount will be different in that case).
Access to AllFramesUpdateCount is so much faster than CurrentSignature, that if you need to track image changes from run-to-run of the application, it will likely be worth computing the CurrentSignature only once at application startup to capture a base AllFramesUpdateCount at that point. Then image changes could be followed by looking at AllFramesUpdateCount during an application run.
CurrentSignature Property
