Install ImageMagick (>= 6.8.0-10) for image conversion:
brew install imagemagick
Install leptonica (>= 1.69) and tesseract (>= 3.02.02) for OCR:
brew install leptonica
brew install tesseract --all-languages
Or install without --all-languages and install them manually as needed.
Make sure the input image is a grayscale .tif and fairly large. ~500x150 was too small, while ~2000*500 worked very well.
convert input.png -resize 400% -type Grayscale input.tif
OCR it. The default language is English. Language codes are 3 chars per man tesseract. French language is coded 'fra'.
tesseract -l eng input.tif output
This creates output.txt.