I noticed that Yandex.Metrica (and Google Analytics too) responds to the gif изображением 1x1 px site with gif изображением 1x1 px (?!) gif изображением 1x1 px . What it is? "Trick" with html ?

Request

 GET /webvisor/32138055?rn=680591080... HTTP/1.1 Host: mc.yandex.ru User-Agent: someua Cookie: somecookie

Answer

 HTTP/1.1 200 OK Server: nginx/1.8.1 Content-Type: image/gif Content-Length: 43 Connection: keep-alive

* some headlines removed specially

Data response length 43b ? But the answer is empty! (Or filled with spaces ?!). Please explain what it is.

    1 answer 1

    Here the task of sending data is performed, and there is no need to receive an answer. When requesting a gif image, the statistics collection server receives all the necessary data. The page on which the image and other data are placed, for example, browser version, cookie.
    By the way, by downloading an empty gif, you can send data to the server (cross-domain request), some security parameters may limit sending data to third-party addresses. Nobody will limit the loading of the picture.