Hello, It really makes no difference where the WIM to be validated resides, it could be on the USB key or another USB external drive.  At the very beginning of the restore process you will be prompted to navigate to wherever the WIM is located.
Hi, how can we move the syspreped image to a Dell Image Assist created USB? Does it go under a particular folder? Does it also save the image locally on the computer where image has been created? Thanks 
Move sysprepped image to USB drive