I did a test with creating a table just for the tile image and the crc32, the table looks like this:

CREATE TABLE testtable ([crc32] VARCHAR (8) PRIMARY KEY UNIQUE, [maptile] BLOB COLLATE NOCASE);

I didn't do anything for coordinates, nothing special to see there.

I ran the test on 213304 map tiles, and at the end, in the database I had 135417 unique tiles (77887 were duplicates!).

The 213304 tiles on my computer use 897MB (size on disk), and the database, after excluding the duplicates is about 290 MB.

I used sqlite3.

-ioan