Have you seen the queries that are used to generate actually useful results rather than just toy demonstrations? They look a lot more like your first example except with more specificity. It'd be more like "an adult human of any gender and any race and skin color dressed in a laboratory coat standing by a window holding a beaker in the afternoon sun. 1950s, color image, Canon 82mm f/3.6, desaturated and moody." so if instead you are looking for an image with a person of a specific ethnicity or gender then you are for sure going to add that in along with all of the details. If you are instead worried about the bias of the person choosing the image to use then there is nothing short of restricting them to a single choice that will fix that and even in that case they would probably just not use the tool since it wasn't satisfying their own preferences.