Is it possible to find out what compression algorithms have been used for images in a PDF document?
You can use
If you open a PDF in a text editor, you'll find a line like this for each image:
This image uses the FlateDecode filter, "a commonly used filter based on the zlib/deflate algorithm (a.k.a. gzip, but not zip)"
This image uses the DCTDecode filter, "a lossy filter based on the JPEG standard"
Filter definitions are from the Portable Document Format Wikipedia page, which has a list of all the supported filters.
However, it can be difficult to work out which image is which in a text editor - the objects do not necessarily occur in reading order. Breaking the PDF into single pages might help here.
I think Enfocus Pitstop Pro, an Acrobat plugin, may well give you this info (along with dimensions, position, DPI etc) in its object inspector, but I no longer have it, and can't seem to find any mention of this specific attribute in their manual.