your find command should work. also, try to use quotes
Code:
find . -iname "*.jpg" -mtime -30
alternatively, if you don't mind using Python
Code:
!#/usr/bin/env python
import os
import time
thirtydays = 86400*30
now = time.time()
directory=os.path.join("/home","user","path") #change accordingly
for r,d,f in os.walk(directory):
for files in f:
if files[-4:].lower()==".jpg":
timestamp = os.path.getmtime( os.path.join(r,files) )
if now-thirtydays < timestamp:
print os.path.join(r,files)