Tk::Photo can be initialised from a file: $widget->Photo(-file=>'some.jpeg').
The manual page tells you that it can also read the image from string data: $widget->Photo(-data=>$data).
Reading the file into $data does not work, not even with binmode. What's missing in the manual page (at least in Version 3.014) is the fact that the string data must be base64-encoded! It's very convenient to use a here-document in base64, but it is not what I expect. I would have prefered to convert a base64 here-document manually before passing it to Tk::Photo.