I had a look at the images. You won't get correct results with this kind of images. Your jet needs to be zoomed in and you need to record with more fps. At the moment there are hardly any particles that are moving. Just three or four particles are in the jet, this is not enough for particle image velocimetry.
Additionally, I just noticed that many of your images are totally identical. Your camera seems to save frame duplicates instead of filming with true 50 fps (e.g. 00146_032.jpg and 00146_033.jpg are identical).