Image size and css size confusion


#1

I am having a problem with how to size images in my app. I am using adobe to create some images and I need to figure out at what size to export them.

I have the following images:

  1. A Full Screen splash screen image
  2. An image which will need to be 100% width of the device screen (my app is portrait only).
  3. A smaller image which comes from Facebook which is 50px.

I want to support all screen sizes so I am confused what size should I create my images as in Adobe? How do I apply css to them so they fit as they are supposed to? Essentially I am looking for the images to look good on any type of screen.