Barcode recognition quality depends on barcode print quality and scanning settings. Below are some recommendations for barcodes to be recognized correctly:

• Barcode must be separated from other text by a fairly wide white gap.
• Barcode size and the width of its separate bars or dots must meet the following requirements:
  • The optimal barcode height is more than 10 millimeters. The size of a barcode should be less than size A4
  • Barcode height must be bigger than the double height of a text line
    
  • For not-square barcodes, their length must be bigger than their height
  • For 1D barcodes, the width of the thinnest bar in the barcode must be at least 3–5 pixels in terms of pixels of the image
    
  • For 2D barcodes, the dimensions of their cells should be at least 2x2 pixels, the recommended size is 4x4 pixels or more. Besides, for all 2D barcodes except PDF417, the cells should be square, because barcodes with the 1x1 cells most likely will be recognized incorrectly
• It is not recommended to compress images of barcodes using JPEG compression as it makes barcode borders fuzzy
  
• It is also not recommended to skew barcodes, i.e. an angle of the barcode should be a multiple of 90 degrees relative to the horizontal axis
  
• The grayscale scanning mode is the best for OCR purposes. When scanning in black-and-white, adjust the brightness setting. If the barcode is “torn” or very light, lower the brightness to make the image darker. If the barcode is distorted or its parts are glued together, increase the brightness to make the image brighter.
• Avoid printing barcodes in frames
  
• Avoid printing barcodes over a text or a picture.
  

In some cases, barcodes which do not fit these recommendations also can be recognized, but the quality of recognition may be poor.