App for photo resample and send to gmail app?

I need to lower the resolution of some photos and send them to the gmail app so that they're used as attachments (I don't use the iPhone mail app, but the gmail app, so I need good connection with the gmail app and not the Mail app)

What would be the most straightforward and easiest way of doing this?

The photos resolution needs to be lowered to 640x480 or so

Thanks!!