Storing different versions of an image vs resizing on request
<p>I am writing an App for android in which the user can upload images. My idea is now resizing the image on client side to the maximal required resolution for xxhdpi. After I send it to the server and on server side I store the xxhdpi version. Now the actual question is if I should either store also copies in lower resolution for xhdpi, hdpi,... or resize the xxhdpi version on request (if a smaller resolution is needed) before sending  it to the client. The objective is neither sending nor storing more data than actually needed and having a good response time and acceptable server workload (because of potentially multiple resizing processes). </p>