Apropos the perennial retina vs PPI questions:
We have an answer to a recent question about setting up an image which, in my opinion, correctly states: "pixels are all that matter." But I have dealt, in a non-professional setting, with web pages where various devices (especially mobile) completely ignored specified units. Are there any caveats that a designer should know about?
I know that the pixel dimensions are all that matters and that PPI is merely a flag in the file header, rather than pixel data.
However in practice, are there times when the PPI flag is honored by iphone/retina/screen-density-aware software if it finds one?
If one provides a 100px square image, one with 10ppi flag set, and one set as 1200ppi, in the absence of implicit style sheets or specification (etc) will the software treat them differently solely due to the ppi flag?