In CS5 and CS6 when you import a image, a reference is created in the library, but is not converted to a "symbol".
Yes, in CS5 when you import an image, such as a png. it is displayed in the library as the original png file as well as a converted symbol. This was changed in CS6 and I need to know if there is a setting to make it work this way.
CS5.5 converts anything imported into a symbol as well. Is this really your desired functionality?
If you're going to use it via ActionScript you need to assign a unique class name you can access in your code anyway. Name all your images uniquely in code class format and import them all to library but expect that flash will not auto-link those symbols for actionscript using .as class files. It's flash's nature to make you tick off the checkbox to export to actionscript and assign each clip to a class manually.