OCR not detecting numbers

I'm trying to use OCR to read numbers from different photos. I have pre-processed the images as seen below, and it just won't detect some even though they look very reading. I've put the pre-processed photos below to show which ones are detected and which aren't.

Able to detect:

Not able to detect:

Also not detected:

[Mathieu NOE]

hello

maybe you'll find some ideas here : Unable to Extract Numbers Using OCR Despite Performing Image Processing - MATLAB Answers - MATLAB Central

Answer 1

[Image Analyst]

Maybe it's too big. Try shrinking it down to smaller images:

%--------------------------------------------------
% Read in original RGB image and convert to grayscale.
rgbImage = imread('72.png');
% Convert to gray level
binaryImage = rgbImage(:, :, 1) < 128;
binaryImage = imresize(binaryImage, 0.1);
imshow(binaryImage);
impixelinfo;
axis on

%--------------------------------------------------
% Find the number
txt = ocr(binaryImage, 'CharacterSet', '0123456789', 'LayoutAnalysis','line')

txt = 
  ocrText with properties:

                      Text: '72...'
    CharacterBoundingBoxes: [4x4 double]
      CharacterConfidences: [4x1 single]
                     Words: {'72'}
         WordBoundingBoxes: [24 11 88 69]
           WordConfidences: 0.5639
                 TextLines: {'72'}
     TextLineBoundingBoxes: [24 11 88 69]
       TextLineConfidences: 0.5639

fprintf('Detected "%s".\n', txt.Words{1})

Detected "72".