Here's a recent Q:

I'm having problems converting medical terms to images. I find myself using lots of people (e.g. an angry-faced man for increased blood pressure, an amputee for diabetes), so my palaces are full of legs, hands, blood, and urine tanks, which gets confusing. What should I do?

Generally I try to pick specific people; e.g. Dr. Cox from Scrubs for HTN instead of just a "angry-faced man." So doing that may help in differentiating people. If you feel like your palaces are all filled with people, I'd just make a more concerted effort to imagine more objects. But it happens. A solid chunk of my images are people. They're just generally more memorable. I'd also add that you shouldn't necessarily feel that your images need to be "true to life." It may work to simply imagine a pair of lungs, for instance, but strange characters or nonsensical objects are often more interesting. For instance, I use Hagrid from Harry Potter to represent blood cells, a bike pump to represent dialysis, Spongebob to represent the lungs, Dr. Cuddy from House to represent UTI, Ron Swanson to represent the central nervous system, etc. They may seem like trivial connections, but they quickly become ingrained with a few repetitions.