Send Reduced lets you share reduced resolution photos by text or email with the minimum number of taps.
This is the Pro version. Try the Free version first to ensure compatibility.
When sharing a photo, just choose "Send Reduced". The first time, you'll have to choose the email (or other) app you want to use with it, but if you set the checkmark to make this permanent, next time you won't even have to do that--as soon as you choose "Send Reduced", you'll be in the email (or other) app.
You can also use Send Reduced to attach a reduced photo--when choosing the attachment from your email app, first time choose the Gallery and set a checkmark, and next time you'll automatically get the photo from the gallery and reduce it.
You can adjust the resolution and quality of the reduced photo by running Send Reduced from your launcher.
Send Reduced Pro is tiny, open source (search the web for source code) and has no ads. It strips identifying information (EXIF and filename) from the photos. This is the Pro version which lets you include some EXIF data and preserve filenames.