I have developed Android application (Application somewhat social media type and this is the first application I have developed) and in that there is a feature to upload images by users. So my question is if any user uploaded any copyrighted or offensive image then who is responsible for it? User or owner of the application developer (in this case me)?
Is there any 3rd party tools needed to scan or verify the images?
Short Answer: Write "Disclaimer"
If you are developing web application which users can upload photos and share them in anywhere they want, you can take those photos' copyrights with yourself or make your users to take that responsibility.
This is where you have to write "Disclaimer" for your application before you give the users access to use your system let them accept your term and conditions and disclaimer so they should be informed that they have responsibility on what they upload.
Also you can have a reporting option where the victim can report the incident so you can review that and delete the particular content from your site.
Is there any 3rd party tools needed to scan or verify the images?
Yes, there are many but how are you going to ensure that the image has copyrights ?
Better, you should be able to catch any of your users on this case.