I load images with numpy/scikit. I know that all images are 200×200 pixels.

When the images are loaded, I notice some have an alpha channel, and therefore have shape (200, 200, 4) instead of (200, 200, 3) which I expect.

Is there a way to delete that last value, discarding the alpha channel and get all images to a nice (200, 200, 3) shape?

Just slice the array to get the first three entries of the last dimension:

image_without_alpha = image[:,:,:3]