I have made modifications to several example OpenCV projects within Android, however I am having some issues with using OpenCV successfully in a new Android project.
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When you add OpenCV from Properties->Android->libarary->Add you need to leave "Is Library" checkbox unchecked. Go to Project->Properties->Android and uncheck "Is Library" and then try again. It should solve your issue (it did for me) but if it doesn't please take a look at the answers of this question as other people have found some other things to be helpful as well.