How can I extract periodic motion from image sequence?

I am working with Laser Speckle Contrast Images and recorded a sequence of images at 30 fps of the forehead. One can clearly observe, a periodic "flashing" occuring as the blood pulsates. I cannot attach data greater than 5MB so I am sharing a drive link (I hope this is alright!)

https://drive.google.com/file/d/15ba92xBm_zY5u1JYol3czGm0fBELi0YF/

However, it is not very obvious and is overshadowed by random noise and artifacts. I know that this flashing is happening with a constant frequency and want to isolate this periodic motion from the rest of fluctuations. I've tried a bandpass filter 0.6 to 2 Hz but the results are not very good. Any help would be appreciated.

Wn=[0.6 / 30 * 2, 2.5 / 30 * 2];
[b,a] = butter(6,Wn,'bandpass');
y = filter(b,a,P,[],3);