How to efficiently print the image of a whiteboard?
For this I use TurboScan on my iPhone.  It's designed for scanning and there are many similar apps.

It takes 3 photos and combines them to get one with good contrast and resolution.  It optimizes for readability.  It automatically detects the edge of the whiteboard and crops there; you can easily adjust the crop to be smaller if desired.  You can easily adjust contrast.

Here is a photo of what's on my whiteboard right now.  This was taken in extremely poor lighting conditions (dim, with lots of glare).  Also, TurboScan outputs a PDF, so you can zoom nicely without it becoming pixelated, but SE would only allow me to upload a JPEG, so what's below is lower quality.  Right-click and open in a new window to see it better.