The irregularity is the scale invariant index which helps to rank fonts by their drawings. The method on assessment of the irregularity of vector fonts was proposed previously. The assessment of the irregularity of rasterised fonts (electronic and printed) represents certain difficulty related to the inability to accurately calculate the perimeter and area of elements of rasterized (bitmap) font. In the work, the method on assessment of the irregularity of bitmap images of rasterised fonts based on ideas of fractal geometry is proposed.