The curved lines in this picture are trails of bubbles formed as charged particles force their way through an unstable mixture of neon and hydrogen. They curve in an applied magnetic field, and spiral because they lose energy quickly.
The highlighted track that curves to the left (red) was produced by an electron while its partner, which turns to the right, was produced by a positron . Together they are referred to as an electron-positron pair that has 'materialized’ from a high energy photon in the electric field of a nucleus. This is often referred to as 'pair-production’.
Notice that the photon that produced this pair was radiated from the nearby electron track, which then curled up (slowed down) after losing the photon .
For full details of this picture, click here.
For other examples of photons click on one of the pictures below