I don't really think that screenshot images should be a major issue. You can take the images from official websites like Samsung, Nokia, Sony. etc. as long as you give proper image credits bro. They just want us to be careful with "Violent content" images and "Underage, non-consensual, or illegal sex" images. Also please take a note of "Trademarked" logos.
They also have a section for "Copyright infringement":