How can you represent binary image data in XML using plain text?

Binary data is represented in XML using Base64 encoding See RFC 1341 Section 5.2. Binary data is a string of numbers in base 2 represented by a series of bits (binary digits). These same numbers can be represented in base 64 using a series of base 64 digits. The convention for representing base 64 digits is to use the upper and lower case letters (52 digits), the numbers (+10 digits), and two punctuation characters '+' and '/' (total = 64).

Since each byte can represent a value from 0 to 255, we would need two base 64 digits to represent it. If we did that, we would need twice the storage to convert binary into plain text. Instead we can convert 3 bytes at a time into 4-digit base 64 numbers. This makes the plain-text representation of binary data "only" 1/3 larger.