Raster Images

Although raster (bitmap) image formats such as TIFF, PNG, GIF ,BMP, JPEG and so forth can be suitable for non-textual content, text inside such image formats is really just a picture of text: it cannot be searched or copied and pasted, and text readers are not able to speak it out loud.

Note that JPEG images in particular use a lossy compression, which introduces artifacts that can be visible and can hinder optical character recognition or other reuse of the files.

Document page-images are most often used in situations where digital versions of original documents are unavailable and paper copies have been scanned. For archival use it’s important to use an image format that is open and standard and that has as few interoperability problems as possible. PNG is better than TIFF in this regard, since TIFF files vary between platforms, but both are better than Windows BMP or PhotoShop PSD (proprietary) or JPEG (lossy).