Algorithm to detect presence of text on image

Solution 1:

There is a standard problem in vision called text detection in images. it is quite different to OCR. OCR concerms itself with what it says, while text detection is about determining if there is text in the image. Adi Shavit's third link is a method to address this problem. You can look on google scholar well cited articles on text detection.

Solution 2:

There are several possible approaches you can take.

1. Use OCR. A search for OCR on Stackoverflow will show many options. These include Tesseract and Ocropus.
2. If your text uses very specific fixed font, you may get away with simple template matching.
3. In the more general case you might want to take a look at "Detecting Text in Natural Scenes with Stroke Width Transform"

UPDATE Jan. 2017
The OpenCV 3.2 contrib module now has a text detection module.
It also includes a sample (C++, Python) of how to use it.