I don't believe you're going to see much compression at all on either the TIFF or JPG files. TIFF files don't compress much, if at all and JPG are already compressed I believe. ONTAP can use either LZO Pro or GZIP compression algorithms, you could try compressing your files with utilities that use these same algorithms to determine compressibility. I think what you'll find is that the only way to compress these file types is at the expense of quality, typically people are keeping TIFF files because they want to retain quality. No storage company should tell you differently either.
ONTAP uses 4 methods of storage efficiency: 1) vol dedupe, 2) vol compression, 3) compaction, 4) cross volume dedupe/compaction. I may have missed one, but it combines those together. Windows doesn't do that for sure. You'll want to use AFF to take advantage of it though as running any kind of compression on spinning rust is a pain point in terms of performance.