need help with Shape recognition and classification

i used this code to highlight only signboard .

figure
I = imread('prj9.jpg');
pic=I(1:size(I,1)/2,1:size(I,2)/2,:);
for mm = 1:size(pic,1)
    for nn = 1:size(pic,2)
        if pic(mm,nn,1) < 80 || pic(mm,nn,2) > 80 || pic(mm,nn,3) > 100
            gsc = 0.3*pic(mm,nn,1) + 0.59*pic(mm,nn,2) + 0.11*pic(mm,nn,3);
            pic(mm,nn,:) = [gsc gsc gsc];
        end
    end
end
imshow(pic)

Now i need to classify differnt shapes such as circle,triangle,hexagon for efficiency purpose pls help with code

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags