I'm not sure about an app to block images and videos, but there are other things you can do to cut back on your data usage. Like turning on data saver mode, turning off data usage for certain apps you only want or use on wifi, turn off auto-sync for certain apps in account settings, auto play settings in apps that display videos, set a usage limit in settings, etc. I'm sure I'm missing a ton of things. A few Google searches can give you a better understanding of how to best optimize your phone for data usage. I'm sorry I didn't really answer the exact question you had, but just wanted to give some tips to help.