Changing the Image Displayed (in a label widget, for example)
FROM:  http://wiki.tcl.tk/876 
(imaged on 2009 mar 19)

(This page has good info on using mmencode to do base64 encoding,
to use in 'image create photo -data ' statements.) 


An obvious solution would be to destroy .display (below) and recreate it.
The problem with this is that the image flickers and is slower.
The easiest and best way for most uses is to instruct the set image to
read another file or configure the image to read different data.

For example #1:
--------------

 #!/usr/local/bin/wish8.2

 #load /usr/local/lib/Img1.2/libimg1.2.so
 package require Img

 global picture
 set picture [image create photo -file picture1.jpg]

 label .display -image $picture
 pack .display

 button .change -text Change -command {new_picture}
 pack .change

 proc new_picture {} {
     global picture
     $picture read ./picture2.jpg
 }

----------------------
END OF SAMPLE CODE #1.

If you are using embedded images you will need to use configure
to change the image.

For example #2:
---------------

 #!/usr/local/bin/wish8.2

 #load /usr/local/lib/Img1.2/libimg1.2.so
 package require Img

 set image1 {
     /9j/4AAQSkZJRgABAQEAAQABAAD//gAuIENSRUFUT1I6IFRoZSBHSU1
     QJ3MgUE5NIEZpbHRlciBWZXJzaW9uIDEuMAr/2wBDAAgGBgcGBQgHBw
     cJCQgKDBQNDAsLDBkSEw8UHRofHh0aHBwgJC4nICIsIxwcKDcpLDAxN
     DQ0Hyc5PTgyPC4zNDL/2wBDAQkJCQwLDBgNDRgyIRwhMjIyMjIyMjIy
     MjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjL
     /wAARCAAUABQDASIAAhEBAxEB/8QAFwABAQEBAAAAAAAAAAAAAAAAAA
     EGB//EABsQAQAABwAAAAAAAAAAAAAAAAACBAUXVJLS/8QAFwEBAQEBA
     AAAAAAAAAAAAAAAAAcBBv/EAB4RAAECBwEAAAAAAAAAAAAAAACS4gEC
     BAUVF1NV/9oADAMBAAIRAxEAPwDECW8q2RJbx8lvKtkSW8fLcXZPRlS
     46PY9PygtpRLeVbIkt4+Qxdk9GVLhsen5QW06WAmhEwAA/9k=
 }

 set image2 {
     /9j/4AAQSkZJRgABAQAAAQABAAD/2wBDABUOEBIQDRUSERIYFhUZHzQ
     iHx0dH0AuMCY0TENQT0tDSUhUXnlmVFlyWkhJaY9qcnyAh4iHUWWUn5
     ODnXmEh4L/2wBDARYYGB8cHz4iIj6CVklWgoKCgoKCgoKCgoKCgoKCg
     oKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoL/wAARCAAe
     AB4DASIAAhEBAxEB/8QAGAAAAwEBAAAAAAAAAAAAAAAAAAMFBgH/xAA
     kEAABBAEEAQUBAAAAAAAAAAABAAIDEQQFEhMxISJhcYGRwf/EABYBAQ
     EBAAAAAAAAAAAAAAAAAAIBA//EABwRAQADAQEAAwAAAAAAAAAAAAEAA
     hEDEiExQf/aAAwDAQACEQMRAD8A2CXPkRY4byOouNNAFlx9gmLPulyN
     U1Pmw7bFj+jcCNxB7IvwjZya8uftV+iXIZ2Tb9l2x21wIqj3/UxTtMi
     1CKZwy5C+MssWQadf70qKo6Q3qVtg7OOG5pb1YpQNNa/TufEzIZeN5s
     SRtJB+x5WgQom/MVOnka/jJGgY87WyzZIla4upjZHHwPgquhCoYZD0u
     3t6Z//Z
 }

 global picture
 set picture [image create photo -data $image1]

 label .display -image $picture
 pack .display

 button .change -text Change -command {new_picture}
 pack .change

 proc new_picture {} {
     global picture image2
     $picture configure -data $image2
 }

-----------------
END OF SAMPLE CODE #2.

(DKF: An alternative technique (if you can afford to keep all
 the needed images in memory) is to simply reconfigure the widget
 that is using the image to use a different image. This is the
 fastest way of switching!)