Realize offline database store image file

1. We could use convas.toDataURL() function to get base64 character,and store those data into sqllite data base
2. Retrieve the hexadecimal data and pass those on the img tag i.e
3. convas.toDataURL() will get as below data:

Reference as below:
1. https://developer.mozilla.org/en/Canvas_tutorial/Drawing_shapes
2. http://en.wikipedia.org/wiki/Data_URI_scheme