Python image art project
Be consistent and pythonic in naming functions.

draw_arrow instead of drawArrow

Use comprehensions instead of creating empty list and appending to it in a for loop. It's both faster and easier to read.

def translate(coords, vector):
    # Translates a list of coordinate tuples over a vector tuple
    return tuple(tuple(map(operator.add, c, vector)) for c in coords)

def mirror(coords):
    # Takes a list of coordinate tuples and mirrors it across the first element of
    #    the first tuple
    # Formula: 2 * base - original
    base = coords[0]
    double_base = tuple(map(operator.mul, base, len(base) * (2,) ))
    return tuple(tuple(map(operator.sub, double_base, cord)) for c in coords)


Why have a function that returns a constant value. Why creating a variable when you can just return the value.

def get_arrow_coords():
    return [...]
# or if you worry about mutability - use tuples. They actually faster if you wouldn't try to modify them (creating new ones from old ones) a lot.

arrow_coords = ...


You can also use collections.namedtuple('Size', 'height width') instead of using plain tuples for sizes. This would improve readability a little.

And I'm not sure, but maybe you would benefit from using numpy as it seems that you're doing some matrices work.