This is an important question for certain contexts.
1) There may be an online web service that allows people to upload images to be OCRed. Some pranksters or bots may start uploading images with no or little text. The OCR engine tries to make sense of the image and wastes immense amounts of CPU cycles.
2) The visually challenged may want to use the computer in this manner: Whenever they have an image with text infront of them, the software automatically recognises areas of text and OCRs it. Post-OCR A TTS system them reads out the text for them.
Now how do we achieve this?
There is a good method. The algorithm is called Run Length Smearing Algorithm (RLSA) . What it does is it smears lines of text into black lines, and then looks for parallel black lines as a sign of lines of text in the image.