Yeah, I figured the server was trying to grab the image. Until I get a chance to look at the code all I can do is guess as to why.
My guesses:
1) Some kind of scan that is checking to see if the URL is valid / a valid image.
2) The Tapatalk plugin being sneaky and annoying.
Post Merge: June 21, 2018, 02:11:31 AM

Bingo

Post Merge: June 21, 2018, 02:28:57 AM
So the forum software has a method that will download the image so that it can determine its dimensions (which seems...a bit wasteful, honestly). The code has a built-in timeout of 0.5 seconds, which is nice, but there are conditions which will break it.
You have a url:
http://obrazki.elektroda.pl/9560129100_1496602879_thumb.jpgIt tries to look up this image, but the image server redirects you to an "https" address. This protocol switch is apparently not handled.
The proper solution would be to figure out how to make it handle this case gracefully. However, this is PHP code and it's getting late here, so instead I just updated the method to ignore URLs from the elektroda.pl domain. Seems to work

Alternatively, you could have used the https address instead of the http address.