It's probably important to note that generally speaking images created, regardless of the method, are not going to be bootable. They require that you boot from rescue media to use them to restore your PC.
In the case of the native Windows System Image utility (which I don't use nor recommend) you will need to boot from the installation media and then use the advance trouble shooting options to find "System Image Recovery"
Other third party resources will generally require that you create a rescue CD from within their software in order to boot your machine and then use their image to recover your PC.