The distance from the bottom right corner of the brick in your image to the top of the plate-part is 67px, which for a plate is 3.2mm. The full distance from the bottom right corner of the brick in your image to the top of the brick is 609px, which equates to 28.78mm, close enough to the 28.8mm a 3 brick-high piece would be (3 * 9.6mm). Well spotted @rschulz
This is not LEGO. Searching for 1 x 4 x 3 on BrickLink does not bring up any Brick, Modifieds that have rounded corners on one side, let alone a bottom plate. Nor are there any 1 x 4 Plate, Modifieds that have an addition like the above.
While LEGO pieces are well served with publicly accessible and searchable parts databases, MegaBlocks and their ilk are not. Your best bet - assuming this is a MegaBlocks part, and the part was stickered in accordance with whatever instructions come with the set - is a laborious search of a MegaBlocks set database, looking for an image of a 2 on a blue part of the model depicted on the box art.