Phash generates same value for every image i.e aa54aa54aa54aa54

[osiloke]

Image.Phash seems to generate the same value for every image i try to hash.
Scenario

im, err := magick.DecodeData(blob)
h, err := im.PHash()

h is always the same value even though image changes. I used to to hash frames in a video file.

[rainycape]

This seems to happen because Convolve() is buggy when using the IM backend. It always generates a completely white image. I'm investigating this problem right now.

[rainycape]

@osiloke Just spent too much time trying to figure out why ConvolveImage() in IM always returns a white image with no luck.

This is not very important to us because we mostly use the GM backend in production, so I'm not gonna spend any more time trying to fix it. However, patches are welcome.