Identifying electron and positron creation using bubble chamber tracks Taken from a bubble chamber track image,

(http://hst-archive.web.cern.ch/archiv/HST2004/bubble_chambers/BCwebsite/media/lesson071.gif)
I have marked several single (unpaired) creation of what I suppose are electrons and positrons:

Are my markings correct indicating the electrons and positrons being created in this image?
When a new unpaired particle is created seemingly out of nothing in bubble chamber images, is the cause always attributed to photon-photon collision, which do not show up in bubble chamber track images?
 A: Can you give a link for the picture so as to know the incoming beam? It is a very noisy beam, I have scanned thousand of the Cern two meter bubble chamber pictures and do not remember such noise.
Assuming that soft electrons and positrons are observed, the electrons may come from neutral particles in the beam interacting with the atoms of the medium of the bubble chamber.

When a new unpaired particle is created seemingly out of nothing in bubble chamber images, is the cause always attributed to photon-photon collision, which do not show up in bubble chamber track images?

No. Photon-photon interaction have very small probability . If it is photons coming with the beam the interaction is with the fields of the atoms of the medium.
Creation of positrons by real or virtual photons means a pair creation, for conservation of charge. At the center of mass the two are of equal and opposite momentum, but depending on the momentum in the lab of the creating photon the Lorentz transformation to the lab may give a very small momentum in the lab for one of them, so it would not have any length of track to be recorded.
