Phones automatically change the file type to better fit their devices.
So let's say they have an updated Android and a file was a PNG the Android device will update it to a JPEG because it uses that file type as it's default.
This is especially true when sharing files between devices.
It's almost likely when you sent the file to your friend or they downloaded it themselves it was downloaded in a different file type.
{At the same time different devices also means that the image EXIF code {the code of an...