Every recipe which compiles the source code and generates the binaries contains certain mechanism which verifies any changes in the License of sources and flags with error if any License changes occurs.
For example, if we mentions following variables for compilation of Linux kernel,
SECTION = "kernel" LICENSE = "GPLv2" LIC_FILES_CHKSUM = "file://COPYING;md5=d7810fab7487fb0aad327b76f1be7cd7"
Yocto verifies the LICENSE files checksum during the compilation process and if everything goes alright, it copies the LICENSE file separately in output directory to easily identify licensing of the source. This License verification is very helpful when working with complex and large number of packages.
tmp/deploy/licenses/kernel $ tree . ├── COPYING ├── generic_GPLv2 └── recipeinfo