Try this:
% Generate sample data
imageArray = [ 3 4 5 5 4 4 5 5 3; 5 4 5 5 3 3 3 3 4];
% Find the max value.
maxValue = max(imageArray(:))
% Find all locations where it exists.
[rowsOfMaxes colsOfMaxes] = find(imageArray == maxValue)
That said, this is probably not what you want to do to find the laser spot. You probably want to either do a spatial filter or a threshold, and then binarize and find the centroid of the binary blob. There are some laser tracking programs in the File Exchange: http://www.mathworks.com/matlabcentral/fileexchange/32492-laser-dot-isolation, http://www.mathworks.com/matlabcentral/fileexchange/33666-simple-particle-filter-demo, http://www.mathworks.com/matlabcentral/fileexchange/17960-particle-filter-color-tracker, http://www.mathworks.com/matlabcentral/fileexchange/31463-simple-demo-program-for-color-based-tracking, etc. etc.
