That line won't correct it. First of all, image() is a built - in function name and you can't use it like "image.*bw" because functions need to be passed arguments.
Next, even if it were a variable name (meaning you blew away the built-in function called image()), then you should try to figure out why you're multiplying two images together that aren't the same size. What would that mean to you? How could you do that?
Next, if you did want to resize one of them, say bw, you'd do
[rows, columns, numberOfColorChannels] = size(yourImage);
resizedBW = imresize(bw, [rows columns]);
mult = yourImage .* resizedBW;
