But I put it off since I was already busy not learning Django...
Then the other day I realized I could just do it in Python using the Python Imaging Library. A few minutes later and it was done.
#!/usr/local/bin/python
from PIL import Image
import sys
src = sys.argv[1]
dst = 'output.jpg'
orig = Image.open(src)
thumb = orig.resize((450,321))
new = Image.new('RGB', (1500,1500))
for j in range(5):
for i in range(5):
new.paste(thumb, (j*450,i*321))
new.save(dst)
Thanks to my friend, the Python Challenge, for making me spend so much time with dear old PIL back in the day.