I have created a mobile application and I am using few graphic wallpapers in that. App is free but I am getting some revenue from Google Ads. Can anyone tell me under which licence I can download and use the images for that app.
If you purchased the images from a stock images website, when you purchased those images you had a few options to choose from for licensing. Read the details of each license and it will be clear which one you will need.
If you just downloaded the images from Google Images or any search engine or website, you might be facing lawsuit(s)... You have to verify that the creator of the image(s) your are using allows you to use them under a license for the usage you need them for.
Another alternative would be to use www.pexels.com where ALL their images are Free for commercial and personal use under the Creative Commons Zero (CC0) license.
You can go with copyright free image search like pixabay, pexels, Unsplash, stocksnap.io, Burst and lot more Check this out https://blog.snappa.com/free-stock-photos/ with CC) license