Here's an example of a full character set font:
All letters must be the same height, and on the same line. You can also have font containing only numbers if you want.
Now that you have your font set up, it's time to load it. You'll get a dialog like this:
Firstly, load your image.
Now if you look at the first image, it starts with a blank character, this character is your space.
So in the initial font char just press space. (You would put 0 if you have numbers only font)
Now in the numbers of font char, You simply put how many characters there are in the font. In the font I gave you, there should be 92 characters.
The character sample is there to make sure all the characters are cutted correctly, make sure you can see whole characters and not fragmented ones.
If that's the case, try changing the number of font char.
Hopefully this cleared it out
EDIT: forgot to mention it... but the letters should ALWAYS be in the same order, this order:
http://www.asciitable.com/ but you can start and stop from where-ever you want.