The datatype would have to be a BLOB. I would also probably have a second field that stored the data type (GIF, JPEG, BMP, etc.)
Basically, what you want to do is load the image in
Java with the Image API. Get the bytes from the image and store them in the BLOB field.
Now you can read the bytes and, based on the data type, use the Image API to reconstruct the image.
Note that this is theoretical only; I havn't actually done this to know how practical/easy this might be.
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