Is it possible to search uploaded images, for example type 'pie chart' and see the images connected to those posts?
Your best bet is to use Google I guess. Try to search like this
pie chart site:https://mathematica.stackexchange.com/
For SE's own tools, no, it's not really possible since images are stored just as that, image files. There's no metadata that describes if an image is a pie chart or anything else.
If users properly describe the alternative text on image markdown as "pie chart", e.g.
![example of pie chart](https://i.stack.imgur.com/i0ey1.jpg)
then it's possible to search for that using SEDE (as of writing, there's none). However, SEDE is updated each week.