In general, if mobile is not something that intestest you, a DPI of 72 or 96 will work. Once mobile and high definition displays enter the picture, a range of images can be provided. To balance overhead and time involved, I am settling on providing an alternate image that is twice the size of the non-mobile image. Implementation will be via the HTML 5 image set attribute.
<img alt="Example Image" src="/images/example.png" srcset="example2x.png 2x" width="600" height="600" title="An example of an image using HTML 5 scrset to provide an image for high resolution displays">
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