In Flex images can be embedded or loaded.
Embedded images load immediately, because they are already part of the Flex SWF file. However, they add to the size of your application and slow down the application initialization process. Embedded images also require you to recompile your applications whenever your image files change.
The alternative to embedding a resource is to load the resource at runtime. You can load a resource from the local file system in which the SWF file runs, or you can access a remote resource, typically though an HTTP request over a network. These images are independent of your Flex application, so you can change them without causing a recompile operation as long as the names of the modified images remain the same. The referenced images add no additional overhead to an application's initial loading time. However, you might experience a delay when you use the images and load them.Learn more about Images and Icons in Flex, and see some examples, at Flex After Dark...
