Target database is storing the images captured by web
spiders including the link where the images have been found.
In target database we use multi-indexing for easy retrieval and
managing the images. There are several fields in the target
database such as image file name, image size, format, and size
in bytes, DC histogram and DC image. Every image from web
spider is inserted into the target database to be evaluated
whether it contains QR code or not. The data required for the
fields is generated, and 8x8 block DCT transform is applied to
every image, which will be used in the data hiding process
module in order to extract the QR code. All fields in the target
database can be used as indexing, and the histogram of DC
image parameter is also used to retrieve the original image
from the source database. For example, if we want to match
whether the image in the target database match any images in
the source database, we can query the source database using the
DC image parameter from the target database. Figure 2 shows
the process to generate DC image of an image.