A method of determining that a finger is in stable contact with a surface covering a sensor area of a fingerprint sensor, the method comprising: on the surface of the fingerprint sensor, receiving the finger having a fingerprint topography; by means of the fingerprint sensor, acquiring a time-sequence of images (n..m) of the fingerprint of the received finger, said time-sequence comprising at least a first image (n) taken at a first time point and a second image (n+1) taken at a second time point which is after the first time point, each of the images being in the form of a two-dimensional or one-dimensional array of pixels, each pixel having an intensity; for each image of the time-sequence, dividing an image area of the image, corresponding to the sensor area of the fingerprint sensor, into a plurality of image regions (r), said regions partly overlapping each other and covering the whole image area; and based on image analysis of each of the plurality of image regions of each image of the time-sequence, determining that the finger is in stable contact with the surface covering the sensor area; wherein the determining that the finger is in stable contact comprises, in at least one of the time-sequence of images, detecting a non-contacted part of the surface of the sensor area by determining that an average intensity value of any one of the regions (r) is affected by a high-intensity part of the image area, corresponding to the non-contacted part, to such a degree that detection of the high-intensity part, and thus the non-contacted part, is triggered, wherein said one of the regions (r) overlaps with neighbouring regions by at least 20% in both dimensions of the two-dimensional image area, said one of the regions overlapping both of two regions which do not overlap each other, wherein for each of the two non-overlapping regions an average intensity value of the region is not affected by the high-intensity part to such a degree that detection of the high-intensity part, and thus the non-contacted part, is triggered. on the surface of the fingerprint sensor, receiving the finger having a fingerprint topography; by means of the fingerprint sensor, acquiring a time-sequence of images (n..m) of the fingerprint of the received finger, said time-sequence comprising at least a first image (n) taken at a first time point and a second image (n+1) taken at a second time point which is after the first time point, each of the images being in the form of a two-dimensional or one-dimensional array of pixels, each pixel having an intensity; for each image of the time-sequence, dividing an image area of the image, corresponding to the sensor area of the fingerprint sensor, into a plurality of image regions (r), said regions partly overlapping each other and covering the whole image area; and based on image analysis of each of the plurality of image regions of each image of the time-sequence, determining that the finger is in stable contact with the surface covering the sensor area; wherein the determining that the finger is in stable contact comprises, in at least one of the time-sequence of images, detecting a non-contacted part of the surface of the sensor area by determining that an average intensity value of any one of the regions (r) is affected by a high-intensity part of the image area, corresponding to the non-contacted part, to such a degree that detection of the high-intensity part, and thus the non-contacted part, is triggered, wherein said one of the regions (r) overlaps with neighbouring regions by at least 20% in both dimensions of the two-dimensional image area, said one of the regions overlapping both of two regions which do not overlap each other, wherein for each of the two non-overlapping regions an average intensity value of the region is not affected by the high-intensity part to such a degree that detection of the high-intensity part, and thus the non-contacted part, is triggered.