To thoroughly check a file name,

• If your file is on the server, from WinSCP right-mouse click the name and choose "Rename" in order to look at each character in the name and to check the extension.
• If your file is on your local computer, from Windows Explorer right-mouse click the image name and choose "Rename" in order to look at each character in the name. To check the file extension, right-mouse click on the image name and choose "Properties" (located at the bottom).