Thumbnail for random category random post at the bottom of my post

[craftpassion]

I don't think I can find this anywhere in the forum, so please help me.
Currently, I am using "LinkWithin" widget to display some random thumbnail photos of my old post at my post end. I want to change this. I want it to display random thumbnail photos related to the category/categories of the post I wrote.
I have done the randomization for one of the categories and place it at the sidebar (thank you guys for helping), but now I want to display randomize category and randomize thumbnail at my post end. Can it be done?
My site is Craft Passion and this is my latest post.
I don't prefer any new plugin to be installed as it will increase my site queries and thus the loading time.
Thank you guys for the help.