Some answers I like:

• How can I determine distance from an object in a video?
• Problem with Precision floating point operation in C
• Bounding ellipse
• Transforming captured co-ordinates into screen co-ordinates
• How to use SIFT algorithm to compute how similiar two images are?
• Shortest path to transform one word into another
• Skewing an image using Perspective Transforms
• Code Golf: Build Me an Arc
• Plotting Bessel function in MATLAB
• Incrementing values in a sparse matrix takes very long

NB: The first person to get a computer-vision & opencv badge :)