Appropriate flag Icon in head of each blog post

My blog is a travel site where I update while I’m on the road. I would like to have a flag of the location the post is about (or written from) next to the head for each blog post. I am still in the design stage, so I have nothing to show you, but I could also put the flag under the head, next to the date etc.

My plan was to use cool little flag icons from famfam as seen here: https://www.famfamfam.com/lab/icons/flags/

Because the flag would be different in each post I don’t know how I can make this work. I’ve seen examples of CSS where an image is next to the head, but no examples where the image changes (unless it’s just type changing on a calendar icon etc.).

I havent seen a plugin that allows this, maybe you guys can point me in the right direction with some CSS. I have very basic programming skills but can learn from example.

Thanks.