Here you mentioned to "load a bitmap image from my form to SQL backup and then retrieve the same image".
You could iterate through all pixels of one image and check if the other image, at identical co-ordinates, returns identical color values.
But I can only guess that at the time you get the image from your database, there is no image on the form to compare with.
Therefore think of creating a checksum (CRC, MD5 or the like) for the image on your form. Store it along with the image in the database.
Then, after retrieving image and checksum from the database, create the checksum again and compare with the one just retrieved.
Identical images should produce identical checksums. Differing images have a very high probability to produce different checksums as well.