Yeah, well you can convert your image's extension through gimp or photoshop.
Or if you are not be able convert your image's extension then you can send your image to me after i will convert your image's extension.
To clarify, changing the file type is not as simple as changing the file extension. The file's extension is part of the file name and is used to indicate the file type. It can be changed simply by renaming the file. However, the file type itself has to do with how data is encoded and is not changed simply by changing the file name. When you changed the name from .jpg to .png, that made the issue worse because now the reader expects png encoding but receives jpg encoding; which is why you get that message.