The problem is that the selected image is being returned as a URI and not as a separate directory and filename.
You would first need to copy the file from the URI returned from the "FileName" property to a local directory like File.DirInternal.
Then you can use that local copy as the source to upload via FTP.
However you may very well run into the problem of not being able to determine the filename from the URI as described here:
For a current project, it is necessary to determine the file name of a file that was selected with the ContentChooser. The file names were previously defined by other users and are relevant for further processing of the file. Based on the solution of Erel and Inman the attached test project was...
So, when you do the copy from the URI to a local directory, you may need to make up a name for the file.