I entered the code (as modified by Uncle Asad) but it hangs Finder every time - I have to relaunch.
This is the code as entered:

tell application "Finder"
set this_folder to (path to application support from user domain as string) & "iLifeAssetManagement:assets" as alias
set target_folder to (path to pictures folder from user domain as string) & "MyStream" as alias
try
duplicate (every file of the entire contents of this_folder whose name contains "IMG") to the target_folder with replacing
end try
end tell

I get this error:
tell application "Finder"
path to application support from user domain as string
path to pictures folder from user domain as string
-- 'core'\'clon'{ 'insh':'alis'($00000000016E000200010C4D6163696E746F7368204844000000000000000000000000000000CB59B162482B0000000E2FB7084D7953747265616D0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000131D7DCB5AD85D0000000000000000FFFFFFFF00000920000000000000000000000000000000085069637475726573001000080000CB5916B20000001100080000CB5A3DAD00000001000C000E2FB7000C3E47000C379E000200344D6163696E746F73682048443A55736572733A00706574657262616…
end tell

Anyone else finding this? Any ideas what has gone wrong? Thanks.