I have been working on this report and I saved and downloaded certain images off the internet to put in my paper. When I was going back to cite them later, I reverse google searched the images by uploading the images to have the search engine find them on the internet. Some of these images could no longer be found. How do I cite the images I can no longer find the sources for? Or should I just find different images?
If you can't find the source at all, you should choose a different image. You can't simply put a citation like:
Image. Found on the internet, source unknown.
Even though it would be nice to be able to do that, that defeats the purpose of having a citation at all, which is so that people can see where you got it.
You might find the following questions useful:
This question that was pointed out in the comments seems to be a case similar to yours, with good advice. Basically you need to somehow track down the source; once you have tracked it down, the specific citation text is not such a big deal, as long as you are listing the source.
This question is also relevant. Unfortunately or not, the culture is extremely pervasive in academia to just go pasting images from the internet without citations (especially Google images, and especially in presentations rather than published papers). This is not completely ethical, but it is common practice.