img=;

?ImageConvolve

?BoxMatrix

img // ImageDimensions

ker[n_] := ReplacePart[((-BoxMatrix[n])/((((2n+1))^2)-1)), {n+1,n+1}->1]

ker[5]

ImageConvolve[img, BoxMatrix[1]/9] // ImageDimensions

ImageConvolve[img // ColorNegate,ker[15]] // ImageAdjust // ColorNegate

img

img//ImageAdjust

img2=Import["http://drorbn.net/bbs/shots/17-1750-171013-121553.jpg"]

img2//ImageAdjust

ImageConvolve[img2 // ColorNegate,ker[15]] // ImageAdjust