Highlight (un)recognized words

[shreevatsa]

Suggested by Suhas: when words get skipped by the OCR, would be useful to know.

Maybe we can draw rectangles around recognized words, or increase their relative brightness/opacity (or whatever), so that unrecognized words get noticed

[shreevatsa]

This should be possible:

• render canvas to image and send image to OCR
• use the response to modify the canvas (e.g. dim everything, and brighten recognized words)
• render this modified canvas to image, and use that for the page backgrounds

[shreevatsa]

Would be good to include bounding boxes for each line, in the line's attrs. This will also help if we want tight bounding boxes for lines/regions later.

[shreevatsa]

Done:

in 25d8516b04a185adb010ad1c76c30fd76f7caf51.

[shreevatsa]

Made the boxes slightly wider in 177f878e1ff2de96d0f6a3c372726f8380b3e53a.