Writing "application/octet-stream" content type response as image/jpeg

Here is what I'm trying to do, which is failing in one case only -

1) Get the remote image via file_get_contents().

2) The response content type is coming up as "application/octet-stream".

3) Write the image into temp directory, Now the saved image is coming up as "application/octet-stream" content type rather than image/jpeg, while the original url is image.

4) Using imagecreatefromstring() returns false with binary data, setting headers is not making any difference.

any thoughts ?