I was told( by a Perl/Tk expert) that the Photo object wants base64_encoded data, and the -file=> option, does convert the binary data to base64 internally as it is read from the disk. So I don't think there is anyway around it.

Thanks. That knocks the final nail in my pursuit of a faster method using Tk.

It seems weird to convert the binary data to base 64 though. It must at some point convert it back to binary to manipulate it and set it into the underlying hardware buffer/device context. Passing it through an ascii-based intermediate format is just pure overhead--though that does explain the rather tawdry performance of Tk image manipulations.