Read a PNG (or GIF) image, filter, and display:

1. Read the grayscale PNG file denise.png into rectangular array A

image = Import["denise.png","PNG"]   or
image = Import["denise.gif","GIF"]
A = image[[1,1]]/255.;

2. Display A.   Display a smoothed (blurred) version of A.

ListDensityPlot[A,Mesh->False, AspectRatio->Automatic]
        -- or --
Show[Graphics[Raster[A]], AspectRatio->Automatic]

blurA = ListConvolve[Table[1/25,{5},{5}],A];
Show[Graphics[Raster[blurA]], AspectRatio->Automatic]

3. Use FFT to smooth A, and display

B = Fourier[A];
      delete higher frequencies
      now invert & display
Show[Graphics[Raster[ Re[InverseFourier[B]] ]], AspectRatio->Automatic]