CHECKSUM replacement for IMAGE

CREATE FUNCTION dbo.fnPesoBinaryChecksum
(
@Data IMAGE
)
RETURNS INT
AS

BEGIN
DECLARE@Index INT,
@MaxIndex INT,
@SUM BIGINT,
@Overflow TINYINT

SELECT@Index = 1,
@MaxIndex = DATALENGTH(@Data),
@SUM = 0

WHILE @Index <= @MaxIndex
SELECT@SUM = (16 * @SUM) ^ SUBSTRING(@Data, @Index, 1),
@Overflow = @SUM / 4294967296,
@SUM = @SUM - @Overflow * 4294967296,
@SUM = @SUM ^ @Overflow,
@Index = @Index + 1

IF @SUM > 2147483647
SELECT @SUM = @SUM - 4294967296

RETURN @SUM
END