Images and videos can be compressed by the device, the software and/or the carrier on the sending or receiving end (for all 3 respectively). The image should default to the maximum size that is less than or equal to the least of all of these possible limiting factors.
For example, if your device has carrier has a maximum of 1MB and your app has .5MB and your device is limited to .75MB, while the receiving device has 1.5, 1.25 and .25, respectively, assuming your image is 600KB, it should send from your device at .5MB (lowest of your settings) and be received at .25MB (lowest of theirs).
Using a different app or different methodology entirely can avoid this, such as uploading the picture to Google+ and sharing it with the person via that service or using dropbox, etc.
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