1. A method for processing image data, the method comprising: providing image data by an image bitmap comprising pixels, wherein each pixel has exactly one pixel color value out of a plurality of color values; identifying, by a hardware processor by row- and column-wise searching of the image bitmap, pixel regions in which at least one pixel with a first color value of the plurality of color values appears, wherein a pixel region is defined in that a spacing between two pixels having the first color value is less than a prespecifiable first value; ascertaining, by the hardware processor, outermost left, right, upper, and lower boundaries of each pixel region, wherein the boundaries are defined as corners of a respective rectangle; constructing a first rectangle that completely encloses each pixel region; selectively combining overlapping first rectangles to form one or more second rectangles until no further overlaps of the first rectangles exists, and continuing combining overlapping rectangles until no further overlaps of rectangles exist; and encrypting, by the hardware processor, the image data to hide sensitive information within the image data from an unauthorized person by overwriting, by the hardware processor, an area of the one or more ultimately combined rectangles with a prespecifiable second color value different from the first color value.