Should I host my images externally?

My site is very visual and as such page weights are relatively large due to images.
I have just migrated over from Blogger and all of my current images are still hosted on Picasa.
I’m just wondering if I’m better off storing future images in Picasa too rather than in my own WordPress library to save on bandwidth and speed up my site?
Or are there better (free/affordable) hosting options?
Thanks.