I don't know anything about that particular messaging app, but you should be aware that MMS message attachments (pics, videos) are routinely transcoded, re-sized, or re-compressed by the carriers. This happens *after* the message leaves your device, and you have absolutely no control over this. The only reason some message apps provide a user preference (for sending) is so that users on limited data plans don't accidentally chew up too much of their data quota.
There are no "standard rules" for this carrier manipulation of your multimedia content - carriers can do whatever they want, whenever they want. And they do. Generally though, smaller messages are less likely to get fooled around with too much (Carriers will aggressively re-size/compress larger images and videos because it saves them in system capacity when the message is sent to the destination handset).
If you want control over how your pictures look - don't send them by MMS. Use any other method.
