Hey @erjieyong,
Thanks for sharing this question!
I know you mentioned that the solution in this thread doesn’t work because you don’t always want to clear all the photos, but have you considered making the submit button for the form just a button that says “Clear Photos”, and then you could have another button outside the form that would be used for the other use case?
Alternatively, I think the reason that your uploaded photos are still in the UI is because the app isn’t rerunning after you’re clearing the photos from session state, so you might be able to use st.experimental_rerun to rerun the app/get the UI to refresh.