Unlike free text retrieval systems, image databases store and retrieve these scanned images as images - they are not first converted to text. This approach offers two main advantages. Firstly, it is faster and simpler to capture paper based data than by using OCR software, which tends to run relatively slowly and requires user intervention to correct mistakes. Unlike text, images can include handwritten notes, diagrams and so forth. A more detailed comparison is contained in Chapter 5 .
Images also tend to take greater amounts of disk space than their textual counterparts.
This can be partly overcome by using either software or hardware compression techniques. The file formats used to store images or pictures are usually called 'graphic file formats', of which there are at least several hundred. The reason for this is partly historical, but also reflects the needs of different hardware and software vendors to maximise the performance of their products.