Android: You don't have to try very hard to take too many photos with your phone. Gallery Doctor will help clean up the garbage by identifying photos that are too similar, or finding the ones that have poor lighting and may not look very good.
The app will run a quick scan of your gallery and divide up photos it thinks may need attention into one of three categories: Bad Photos, Similar Photos, or Photos for Review. Bad Photos are any images that look like they may have had poor lighting or generally not be very useful. Similar Photos collects any pictures that look too much like each other. The third category allows you to manually review all your photos to see if there are any others you want to get rid of.
The app will also helpfully show you how much space is taken up on your phone by pictures, and how much space you have remaining.