Unfortunately, the image description is simply an argument to a template. CirrusSearch doesn't do anything at that level and can't be that specific. Something like insource:kathmandu
would require the wikitext source to have the word kathmandu in it, but it's not a great substitute.
Regarding filtering by uploader, I'm not too familiar with how the P170 there is structured, but with structured data available it seems plausible the appropriate information could be indexed. Today though P170 is indexed as a plain statement and does not include any context about it. The best workaround i could provide is that the Information template used on many images renders such that the searching for "Author <name>" , with the quotes, tends to bring up only pictures from them.