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- 1 Have you made use of these resources to help you learn to use the AI2 tools. A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook http://www.appinventor.org/book2 ... the links are at the bottom of the Web page. The book 'teaches' users how to program with AI2 blocks.
There is a free programming course here http://www.appinventor.org/content/CourseInABox/Intro and the aia files for the projects in the book are here: http://www.appinventor.org/bookFiles
How to do a lot of basic things with App Inventor are described here: http://www.appinventor.org/content/howDoYou/eventHandling .
Also look here App inventor español. Offline. Tutorial. Ejemplos. Instalación. Códigos. Juegos. Curso gratis de App inventor. and here Tutorial Index | imagnity for more tutorials.
Learn about components Component Reference
and visit the Library The MIT App Inventor Library: Documentation & Support Help>Library on the MENU
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Ok, someone probably can help you with that if you ask a specific question here in the community. I am not able to work with that extension.
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If you ask specific questions about programming, someone in the community will certainly provide advice. 
There are currently several active 'project' discussions in the community. The method could work for you too.
I am glad to help answer specific questions and provide advice.
As I look at the Project you scoped out on Unity that failed miserably I suspect that model will fail using App Inventor 2. Continue trying to count fish but you have to know what App Inventor 2 is capable of doing. What you want to do and what you can do are different things.
A simple model would be to:
- count the bags of the catch
- empty one bag on a tarp to see what an 'average' bag might contain
- photograph the tarp ... this allows one to count the individual fish by inspection or if the dimensions of the tarp is known, compared to similar images of known count.
- multiply the number of bags by the fish count on the tarp???
Uses two photos.
Perhaps 
Do you have a Project plan? What do you expect to do?
Has some organization requested an app like this is or this is something you thought of? If the app exists, what indications do you have that it would be used? What happens to the photos and information once it is uploaded? Who is going to use this data?