UFN_GETIMAGEMIMETYPE

create function dbo.UFN_GETIMAGEMIMETYPE( 
    @imagefile as varbinary(2) )
returns varchar(max)
begin
    declare @header as integer;
    set @header = cast(@imagefile as integer);

    if @header = 16973
        return 'image/bmp'
    if @header = 35152
        return 'image/png'
    if @header = 65496
        return 'image/jpeg'
    if @header = 18249
        return 'image/gif'
    return 'image/jpeg'
end