Is it permissible to record a woman's voice for explanation on a medical educational website, or to display images of women with their faces uncovered to show disease symptoms on the face when no images of men are available?

A woman's voice is not inherently awrah (private/uncovered). What is forbidden is to speak in a soft and alluring manner, based on the Almighty's saying: (Then do not be soft in speech, lest he in whose heart is disease should covet). As for images, it is absolutely forbidden to post pictures of women. Posting pictures of men is permitted under three conditions: obtaining their permission, ensuring their awrah is not exposed, and if there is a benefit in publishing them.