How can one struggle against the whispers and images that cling to the mind? Is it better to ignore them and focus on worship or other things, or to try and forcefully remove them?

The cure for waswasa (whispers/obsessive thoughts) is to completely ignore them and not dwell on them. Occupy your mind with what distracts you from thinking about them. For whoever pays no attention to waswasa, it will disappear after a short time. As for whoever listens to them and acts upon their dictates, they will increase until they drive him to the point of madness.