Check these links to read more.

US National Center for Accessible Media's Collection of Training and Resources for Image Description 

NCAM provides a growing collection of free training and professional development resources. Includes webinars, guidelines, and links to professional development.

The Smithsonian Design Museum - Cooper Hewitt Guidelines for Image Description  

Cooper Hewitt’s Guidelines for Image Description is a living document. The design tools here, like all creative resources, must continue to be tested in various environments and discussed broadly. These guidelines are created to be both comprehensive and responsive to provide guidance while maintaining fluidity to evolve. Paramount to this is the recognition that language is deeply rooted and understood through the context of the culture and society of its time. This practice must continue to be engaged with contemporary dialogues as image description inherently intersects with questions of race, gender, and identity.