Creating own image is easy - only few variables needs to be set:
IMAGE_BASENAME to give a name for your own image
PACKAGE_INSTALL to give a list of packages to install into the image
RDEPENDS to give a list of recipes which are needed to be built to create this image
IMAGE_LINGUAS is an optional list of languages which has to be installed into the image
Then adding of the image class use:
inherit image
And the image recipe is ready for usage.