Previously I discussed on how to extract text from files PDF, CHM and DOC by using software such as text mining tool but for extracting text from images we need a special kind of software that has the OCR technology which can scan the images such as JPG, BMF and provide the text on it.
If the quantity of text on the images are less then you can do it manually but for bulk images or company work you have to make use of OCR technology. OCR is Optical Character Recognition which will transform the JPG images into computer understandable form i.e, it will analyze the picture images, detect the text form and convert, get processed in the computer. The resulting output will be in the text format.
You can also try out softwares that are developed on the optical character recognition concept. There are commercial software such as ABBYY FineReader, Time snapper that make use of ocr technology and ocr plugin integrated software which will extract text from images with utmost accuracy.
As far as I know there are no freewares available which will convert bulk jpg images into text or extract a specific text from the images. But if you have the images in softcopy form then make use of the scanner software. Most of the scanning software has scan by ocr which determines the text from the scanned document or picture images.