Overlay image transparent on app (gopro-app)

I´m an animator and graphicdesigner and it would be helpful to have the option (an app) to put an image semi-transparent over all which is shown on my smart-phone (Or on the gopro-app in the background). If you can tell me where I can get an app like this or someone could program it for me would be great! Since I´m an animator and graphicdesigner I also can help you with my skills. Greetings! Stefan info@basementpictures.com