How do I convert a TTF into individual PNG character images?

You can use Python with FontForge, it has a Python 2.7 interpreter.

On Windows: after installing FontForge, locate the "bin" in installation path and add it to the Windows system path, in my case it is:

c:\Program Files (x86)\FontForgeBuilds\bin\

This dir contains ffpython.exe so after adding it to PATH you can directly run a .py script in console.

> ffpython myscript.py

To export all glyphs you can use this simple script:

import fontforge
F = fontforge.open("perpetua.ttf")
for name in F:
    filename = name + ".png"
    # print name
    F[name].export(filename)
    # F[name].export(filename, 600)     # set height to 600 pixels

documentation:
http://fontforge.github.io/python.html#Glyph
http://fontforge.github.io/python.html#Font

This may be an old question, but I found the following batch file works with ImageMagick 7:

@ECHO OFF
set f=wingding.TTF
set ps=400
set bg=white
set ext=png
set s=600x600
set alpha=A B C D E F G H I J K L M N O P Q R S T U V W Z Y Z
set num=0 1 2 3 4 5 6 7 8 9
For %%X in (%alpha% %num%) do (
convert -font %f% -pointsize %ps% -size %s% -background %bg% label:%%X 
%%X.%ext%)
pause
exit

NOTE: This conversion only works with a limited selection of font characters. It works well for all capital letters. Just install ImageMagick and make sure it is in your environment path. Include "legacy" commands in your installation.