I am working on a program to detect the tips of a probing device and analyze the color change during probing. The input/output mechanisms are more or less in place. What I need
I have used a commercial tool called HexSight ( http://www.lmi3d.com/product/hexsight ) in the past in a very similar application. We were pretty happy with its performance and accuracy.
If you're looking for something very rough/basic you can try caluclating the cross correlation between a reference image and the image you're looking at. An alternative (which is what HexSight uses) is to start with some edge detection algorithm before attempting to find matches to the reference image. In either case, you can follow up with some refinement algorithm once you have a rough candidate. Given that you are trying to find some particular target type you may be able to apply some heuristics or take advantage of the specific target with a custom algorithm.
Here's an idea for a custom solution, assuming the crosses are evenly spaced, on a grid, and the image is not too distorted:
Under the assumptions this should be fairly robust and accurate because it uses information from the entire image. It will not be too sensitive to any local issues, it will even work if a target (or a few) is completely missing or obscured.
Having good optics and illumination are pre-requisities to getting high quality results out of any system. The image you've attches doesn't look that great.