I'd take an image with the sun in view and then find out how bright it is and it's size. Then threshold the image and look for items roughly that bright and that size.
grayImage = rgb2gray(rgbImage);
binaryImage = grayImage > someValue; % someValue is some value that the sun is ALWAYS brighter than.
[labeledImage, numBlobs] = bwlabel(binaryImage);
props = regionprops(binaryImage, 'Area');
allAreas = [props.Area]
sunBlobs = allAreas >= minAreaForSun & allAreas <= maxAreaForSun;
if sum(sunBlobs) >= 1
% There is a sun in the image.
fprintf('Direct Sun at %s\n', datestr(now));
else
% There is no sun in the image.
fprintf('No Direct Sun at %s\n', datestr(now));
end
Attach photos of "with sun" and "without sun" if you need more help.
