Images are effective to the extent that they link information.
Images are not inherently superior to words and bizarre images are not necessary recalled better than common images.
Imagery is chiefly effective when used with an organizing structure.
Most mnemonic strategies are based on imagery.
There is no doubt that imagery can be an effective tool, but there is nothing particular special about imagery. The advantage of imagery is that it provides an easy way of connecting information that is not otherwise readily connected. However, providing verbal links can be equally effective.
The critical element is that words or images provide a context, which links the information. Thus, imagery is only effective when it is an interactive image – one that ties together one bit of information with another.
Visual imagery on its own is of limited value without an organizing structure, such as the method of loci or the peg word method.
It’s usually empathasized that bizarre images are remembered much better, but there is no evidence for this. In many studies indeed, ordinary images are remembered slightly well. One of the problems is that people usually fine it harder to create bizarre images. Unless you have a natural talent for thinking up bizarre images, its probably now worth bothering about.