The JPG image is given by the server as a transparent GIF 1x1 px

For the first time in my practice, faced with such a problem:
On the server is the image in JPG format, say, 100x100 px. If this image used via a browser, the output we get a GIF image 1x1 px. If again to pick up on a local machine via FTP — everything opens as it should. Server nginx. Law — 644.
In fact the essence of the question — maybe someone knows why this could happen?