Hi,
Image without an extension cannot be displayed in UX, but with the wrong extension like .png even if the image is .jpg works.
Follow this steps to generate the problem:
1. save .jpeg image file via FileSystem on device with .png extension
2. in UX show Image via File which points to .png file saved from .jpeg
3. save another .jpeg file via FileSytem and save it as image file without an
extension (remove .png extension from _urlToHashFileName()) and try to use it in UX - this way it will not be displayed.