I'm building a REST API that will be used by native Android and iOS apps as well as HTML5 in Browsers.
I have several images that will be sent in some API calls. I want to generate some thumbnails so that every device gets the proper image size (smaller devices will get smaller pictures, and so on). I couldn't find any information regarding which sizes most people are using.
I would like to know which sets of resolutions are reasonable (or usual) to use.
Bootstrap extra small should be good choice. It works fine for both browsers and phones.
Extra small has auto sizing, the container width should be < 768px. If you don't want auto sizing you can use bootstrap medium, minimum column width is 60px.
Check out the grid options in below link, this should give you some idea on how to proceed.