Return window related information.
http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/winfo.html
See wm for Window manager related information.
Notice that the return value of [winfo id ...] is the id used by toplevel and wish in
toplevel ... -use $id
and
wish ... -use $id
Here's an example:
label .t1 -text Above
label .t2 -text Below
frame .holder -container 1
pack .t1 .holder .t2
exec wish other_application.tcl -use [winfo id .holder] &[Include an image here.]