Bitmap images (BMP) are rarely used on the web due to their bulk, but they can come in handy for hiding data. I will examine two tools that will allow you to store any file in BMP images.
1. BMPWrap: It’s a no fuss portable application that generates bitmap images from any file that is dropped onto its icon and spews out the original file from the image when required. The generated image looks very random and most of the time is composed of random lines of different colour.
Many e-mail providers don’t permit exe, dll etc as attachments and attempting to send these files simply results in bounced mails. Changing the file extension sometimes work, but not always. BMPWrap’s objective is simple – to fool the mail server into thinking that the file is actually an image file. Using this technique you can also upload your files to various image hosts. BMPWrap doesn’t provide any encryption so it’s not ideally suited for hiding sensitive data, but still it’s safer to have a random bmp image lying around than a text file with passwords.
2. SteganoG: This portable freeware is intended for hiding sensitive data through Steganography. You need to supply SteganoG with both the image and the data file that needs to be hidden. SteganoG hides the file without modifying the appearance of the bitmap file. However, keep in mind that the size of the file SteganoG can hide is dependent on the size of the bitmap image you provide. So, if you intend to hide a large file you need to supply it a big bitmap image. SteganoG takes security pretty seriously and offers multiple methods for encrypting your data including RC4 and Blowfish.