Attached Images - Poor Quality

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21

Ahah! I was just about to ask if you were on a phone/mobile connection via Sprint or Verizon.

Recompressing images (lossily) is most definitely something that the carriers do to save themselves some bandwidth.

The difference you’re seeing (Discourse vs. Dropbox) can actually be taken a little farther - HTTP vs. HTTPS. They won’t (can’t) intercept and rewrite images over HTTPS connections.

To test for sure, try the following commands:

$ wget /uploads/default/original/3X/3/9/39e2283b7b26324ffb88f98431e9d17cd1b15587.jpg -O http.jpg

$ wget /uploads/default/original/3X/3/9/39e2283b7b26324ffb88f98431e9d17cd1b15587.jpg --no-check-certificate -O https.jpg

$ sha1sum http.jpg https.jpg
fd73d5db8d3b341617dbd6d0a42e4b51c6846574  http.jpg
fd73d5db8d3b341617dbd6d0a42e4b51c6846574  https.jpg

If you try this and get different results for the file retrieved over http, there’s your smoking gun.

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22

yes, i’m on sprint and yes, those two files are different… the one coming from https is clean.

so… smoking gun indeed! :smile:

@sam @discourse @zogstrip
sorry for sending you guys down the wrong rabbit hole but hopefully this exchange will make it easier to deal with the next person who complains about this

thanks to everyone else who had a look.

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  • Question
  • Hypothesis
  • Prediction
  • Testing
  • Analysis

SCIENCE WORKS, PEOPLE! :grinning:

If it continues to be a problem, it could be alleviated by switching the CDN to HTTPS.

Can you rerun the wget commands with -S (to show headers)? I’d be curious to see the result:

  HTTP/1.1 200 OK
  x-amz-id-2: Z4VWDZjG8MogNbWsoO8fDCR8dlwqEesyUfSJDypmUJgjyvXJC0bZZw1TSm7hAy31
  x-amz-request-id: 8B02A4D3D9D8F91C
  Date: Mon, 07 Apr 2014 18:43:18 GMT
  Content-Disposition: attachment; filename="pointLight_error2.jpg"
  Last-Modified: Mon, 07 Apr 2014 05:08:14 GMT
  ETag: "5b072fe4ee28a9fd1269602848fb7f99"
  Accept-Ranges: bytes
  Content-Type: image/jpeg
  Content-Length: 30337
  Server: AmazonS3
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well, all i can say is when re-reading this thread via a computer which isn’t on the sprint network, it’s pretty funny

all of my comparison images look the same… :smile:

if it’s easy and/or doesn’t introduce any problems or other issues then @supermathie’s suggestion would be appreciated… otherwise, it’s really no big deal to me anymore now that i understand what’s going on… (well, it sort of bums me out about sprint but oh well)

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25

This was a fascinating mystery!

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