It should work even without specifying the path.
Your 3rd option (where you wrote out the full path) doesn’t work because you used backslash instead of a forward slash. backslash signals an escape sequence.
I don’t know how your files are set up but this probably means something is named incorrectly. Check that:
- The data folder is named correctly
- The file is named correctly (This is case sensitive)
- You have the correct file extension (.png, .jpg etc)
I know that you may have already done all this (and if that’s the case I’m probably just frustrating you 
) . If there are no other visible problems I would just try it with a different picture. Try to isolate where exactly is the problem.