The situation being described here is that within a slideshow presentation, there are images of people that the presenter wished to describe audibly to viewers. There is already text being provided to give background information on the people being displayed, but a detailed description of the person’s appearance and setting is desired. The question being, “How long and how detailed should the description be?” The answer to this question is situational, meaning it is not going to be exactly the same for all instances of images containing people. What this means is that in one photo of a person, the location/background may be relevant and important information to provide to the viewer.
Depending on the context that the image is used in, different information from the picture may not be considered “meaningful” content. For example, if the photo shows a headshot of someone with a plain background, the description could just be of what the person looks like. But if it shows the person performing an activity or at a specific location (such as “skiing” or “on the beach”) this could be important information to include. Please note that when describing what someone looks like, we recommend discussing this with the person in the photo first. Either to ask them to describe themselves or to confirm that they are comfortable with the description that has been provided.
In summary, the length of the description is specific to each photo and the amount of content within said photo that is seen as meaningful information. If the desired outcome is to simply show what the person looks like, then the description should do just that. If the purpose of the photo is to show more than that, such as hobbies, location, etc. then this should also be included. The main focus shouldn’t be on the length of the description, so long as all essential information being conveyed visually by the image is also communicated via the description. However, a clear and concise description that achieves these goals is considered best practice to reduce cognitive overload as a result of an excessive description.