I've used the PLUGIN "Simple Image Widget
" to add images to widgets. I find this is easier than using the text widget & using html code. You can use it multiple times to place multiple images if needed. However, there is no "Upload" in this widget, you must already have uploaded the images and know the url to them.
However if you need one that includes an upload function, you may want to try out "Image Widget
" but I believe I had problems with this one, when I tried to use a plugin that hid certain widgets on certain pages. I think because it uses an old type of coding, but I'm not sure. It worked for me to place images, but it didn't work when I needed to hide them on certain pages. Just a FYI.