How to recognize this simple captcha?
For simple things that you might just run the median filter and ocr.
The media filter will, for each pixel in the image, look at the area around it, usually a 3x3 or 5x5 pixel area, determine the average pixel value in that area, and set the pixel to that median value. Nothing will happen in a block of the same color, the entire area will be the same color as the pixel in question, so the median i will be the same as the current value (or at least almost the same resolution allows slight color variations. On the other On the other hand, the noise is pixels, that is, one pixel with another colored area around it will simply disappear, since the median value of the area will be the color of all pixels around the noise pixel.
As for ocr or optical character recognition, I would just use an existing program / library, it would certainly be possible to write an ocr algorithm in Matlab, but that would be much more than writing a simple algorithm in an hour. First you need to read the instructions and algorithms of the ocr.
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For the very simple: read the image as grayscale, threshold, clear and run it through the ocr program.
%# read the image
img = imread('http://internationalpropertiesregistry.com/Server/showFile.php?file=%2FUpload%2F02468.gif358455ebc982cb93b98a258fc4d6ee60.gif');
%# threshold
bw = img < 150;
%# clean up
bw = bwareaopen(bw,3,4);
%# look at it - the number 8 is not so pretty, the rest looks reasonable
figure,imshow(bw)
Then find out if there is an OCR program that can help, like this
For even simpler:
%# read the image
[img,map] = imread('http://internationalpropertiesregistry.com/Server/showFile.php?file=%2FUpload%2F02468.gif358455ebc982cb93b98a258fc4d6ee60.gif');
%# display
figure,imshow(img,map)
%# and type out the numbers. It going to be SO much less work than writing complicated code
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