Responsive or Adaptive Images
Sooner or later I will have to come to grips with images for responsive sites. Here are some of the modules for Drupal 7 that I have tried and some references to the projects and what smarter minds have to say about the responsive/adaptive problem.
Here on pchousekeeping I have tried the Picture module with the required Breakpoints module. It's in Drupal 8 already, but it seems difficult to use. Also tried Adaptive image and Client-side adaptive image modules. Of the three Adaptive Image is my favorite so far.