Pic size is fairly forgiving these days: For this forum it's 1280 pixels in width, 1280 pixels in height or a file size of 1mb.
There are several free software options for reducing pic size/bandwidth:
http://www.vikingsword.com/vb/showthread.php?t=3248
(An update on apps for mobile phone users might be good, I guess. Any tips to share?)
Regards,
Kai