Inconsistent image caching (i0.wp.com) sizing issue (built-in "Photon" function)

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  theoffalo · Member · Feb 25, 2015 at 8:16 am

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  I understand the fact that WordPress.com will cache images that are hotlinked (e.g., src=”http://notonwp.com/image.jpg” becomes http://i0.wp.com/notonwp.com/image.jpg), but I noticed that it was resizing some of the images when it cached it.

  I am testing wordpress.com to replace my own hosted WP blog (keep hitting the White Screen of Death, presumably from PHP running out of memory on my shared host), where I link to images hosted on Instagram by using the media path, e.g., src=”https://instagram.com/p/zCJCg_g-hv/media?size=l”, which displays a 612×612 image.

  When I added an image in this way to my test WordPress.com blog, it rendered it as a 306×306 image the first time: src=”https://i0.wp.com/instagram.com/p/zCJCg_g-hv/media?size=l”. However, subsequent times, it does seem to link directly to the original URL at the original size instead of using the i0.wp.com image.

  Also, when I go directly to the Instagram URL with “media?size=l” appended to it, Instagram does redirect to an actual static .jpg file, but it may point to multiple sources. For instance, the above Instagram URL points to either of these URLS:

  https://igcdn-photos-f-a.akamaihd.net/hphotos-ak-xaf1/t51.2885-15/10995201_446241642199149_1739029708_n.jpg
  http://photos-f.ak.instagram.com/hphotos-ak-xaf1/t51.2885-15/10995201_446241642199149_1739029708_n.jpg

  Both hosts identical pictures. If I hotlink those static .jpg URLs on WordPress.com, the instagram.com-hosted .jpg gets the i0.wp.com treatment, but the akamaihd.net-hosted .jpg links directly.

  So my questions are: Should image caching be resizing images as it was doing in my first attempt? Why do some hotlinked images get cached while others don’t? What’s the relationship between image caching when previewing a draft vs. a published post?