With ImageHide you can indulge in steganography - that is, hiding text within an image, which is only viewable to others with a copy of ImageHide.

Simply open an existing image inside ImageHide, enter the text you wish to hide inside the image and then press the encrypt button. The text is then seamlessly hidden inside with no change to the file size.

It offers support for the most common image formats including TIFF, BMP, GIF, JPG, PCX, PNG, WMF and TGA. It can open and save images in all these formats, but bizarrely warns against saving in the JPG format as this results in loss of data - so why offer the option of saving in this format?

It comes with no instructions so may result in some trial and error at first, and the encryption method isn't that complex, but it is okay for personal use.