There are many ways to do this. One straightforward approach: convert the number to a string; step through the string one character at a time. Arrange for your numeric images to have names like "imageX.png" where 'X' is the number it represents, like 'image3.png'. Now, append your character to "image" and append ".png" to that, and you're done.

You can also convert the character back to an integer and store your images or their names in a suitably arranged array. You could also skip the integer/string conversion altogether with some minor arithmetic.