I guess it would depend on what your are calling a "USB Image" and what you used to create the "USB Image".
Typically images that you create are not bootable but require a "rescue disk" created with the same software.
For instance in the case of an image made with the native Windows software, you would boot from the installation media.
On the second page after choosing a language and keyboard layout, you would use the advanced trouble shooting menu to select "System Image Recovery"
Likewise in my case, where I use Acronis True Image, I boot from the disk I created from within Acronis and then use the Recovery options on it to browse to my Image that I created using Acronis to recover it.