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I have a WordPress site and I recently noticed a strange effect on the site’s images. They look pixelated despite the perfect size as they are not stretched even if I download the image and open it in a normal image viewer it remains pixelated.

I’m using a 3G dongle with my laptop so I thought it was due to the low speed connection so I tested it at work with an optical fiber connection but it looked always pixelated.

But when I browse the site using TOR Browser the images look clean and as expected.

Below are the screenshots:

enter image description here

Now is there a possible explanation to that?

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You state this:

I’m using a 3G dongle with my laptop so I thought it was due to the low speed connection so I tested it at work with an optical fiber connection but it looked always pixelated.

I am not too sure who your 3G provider is or work ISP provider is, but this all sounds like proxy servers somewhere on the network connection reprocessing images to save bandwidth. I have see this happen in the U.S. on my Sprint 3G/4G connection at times. One day images from anything look downscaled. The next day, nice and clear. No explanation ever given or clearly explained.

Many ISP’s deny that they are doing downscaling of images to deal with bandwidth bottlenecks because the implication is they are tampering with “common carrier” data which would negate the concept of net-neutrality; where users pay for service speed and expect the content to be cleanly delivered to them without tampering. But no matter what the ISPs say there are many discussions online—like here and here—pointing to the fact they many ISPs engage in this practice.

The interesting rub here is you do mention the same blockiness on your work connection as with your 3G. If you are 100% sure that is the case, could it be that your 3G provider and work ISP provider are the same entity? If that is the case, that explains that. If not, then next guess would be some national level internet proxying that would be filtering all content. That would explain why when you use TOR—which is essentially a VPN that makes your main connection be anywhere else in the world—the images look fine.

But at the end of the day, something in the chain of network connectivity is reprocessing those images.

And if you want to attempt to diagnose this on your own, just use curl -I from the command line to view raw headers for assets. For example, I am in Brooklyn, New York in the U.S. and this is what I see doing a curl -I from the terminal window of my Mac Mini running OS X to the source image from your site that you mention in your post:

curl -I http://topten.tn/wp-content/uploads/2014/07/Maybach-Exelero.jpg

And the output is as follows:

HTTP/1.1 200 OK
Content-Type: image/jpeg
Server: Apache
Last-Modified: Tue, 29 Jul 2014 11:44:22 GMT
Cache-Control: max-age=900
Expires: Sat, 06 Dec 2014 18:29:25 GMT
Content-Length: 24261
Accept-Ranges: bytes
Date: Sat, 06 Dec 2014 18:26:59 GMT
Age: 754
Connection: keep-alive
X-Geo: varn30.rbx5
X-Geo-Port: 1013
X-Cacheable: Cacheable: matched cache

The Cache-Control header shows a max age of 900. Which is 900 seconds. Which translates to 15 minutes. If you clear the cache on your browser and reload the page, a new image should load. So to my eye, caching is not an issue here. But if someone on the network chain is mucking around with resizing JPEGs via a proxy, the headers could be different.

Again, this curl -I isn’t guaranteed to provide you with a “smoking gun” since for all we know the proxy server is simply compressing the image and transferring source item headers without modification. But it is worth checking if you are interested into getting deeper into what may be causing this issue.

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