How to crop an image by its mask [duplicate]

Question

I have this image:

And for the beard, I have this mask:

I want to cut the beard out using the mask with a transparent background like this:

I followed this SO post's attempt. Here it is:

for img in input_images:
    gaberiel = Image.open(path + '/gaberiel-images/' + img)

    beard_mask = imread(path + '/gaberiel-masks/' + 'beard_binary_' + img[:-4] + '.png', cv2.IMREAD_GRAYSCALE)

    gaberiel_x, gaberiel_y = gaberiel.size
    beard_mask_x, beard_mask_y, _ = beard_mask.shape

    x_beard_mask= min(gaberiel_x, beard_mask_x)
    x_half_beard_mask = beard_mask.shape[0] // 2

    mask_beard = beard_mask[x_half_beard_mask - x_beard_mask // 2: x_half_beard_mask + x_beard_mask // 2 + 1, :gaberiel_y]

    gaberiel_width_half = gaberiel.size[1] // 2
    gaberiel_to_mask = gaberiel[:, gaberiel_width_half - x_half_beard_mask:gaberiel_width_half + x_half_beard_mask]
    masked = cv2.bitwise_and(gaberiel_to_mask, gaberiel_to_mask, mask=mask_beard)

    tmp = cv2.cvtColor(masked, cv2.COLOR_BGR2GRAY)
    _, alpha = cv2.threshold(tmp, 0, 255, cv2.THRESH_BINARY)
    b, g, r = cv2.split(masked)
    rgba = [b, g, r, alpha]
    masked_tr = cv2.merge(rgba, 4)

    plt.axis('off')
    plt.imshow(masked_tr)

But this is the error I am getting:

gaberiel_to_mask = gaberiel[:, gaberiel_width_half - x_half_beard_mask:gaberiel_width_half + x_half_beard_mask]
TypeError: 'PngImageFile' object is not subscriptable

I think that my attempt is overall bad. Is there a way I can simplify this process?