Computer Vision Analysis

That seems a bit tricky, unless you can simplify the problem a little. Now is the text handwritten or printed ? And is it front facing (parallel to image plane). The simplest would be to use a OCR or character recognition application (with perspective distortion, if it is not parallel to image plane) and create a score, which can be tresholded. If there are many characters, the accuracy would increase. But it might be pretty computationally intense, unless you have an approx "scale" of the characters, because you are searching in scale, location, and perspetive distortion, which can be a huge space to search.