Base64 is encoding that allows files or data to be embedded in media that otherwise does not allow certain data. For example, binary files, such as images, often contain bytes that can interrupt an e-mail transmission, so attachments are often base64-encoded (using MIME) so that this binary data converts into a friendlier format. This format only contains the ASCII characters 'A' through 'Z' (upper and lower case), digits '0' through '9', symbols '+', '/', and '=' for padding. This adds up to 64 different values, hence the name base64. Base64 encoded data must be decoded in order for the computer to understand the original data.