Thanks All. I eventually found a Python script to convert image files to base64. Here's a snippet if it helps someone in the future, works quite well and very simplistic:
Python code:
import base64
with open('C:/temp/myimage.png', 'rb') as x1, open('C:/temp/myimagebase64.txt', 'w') as x2:
base64.encode(x1, x2)