Photons, traditionally regarded as elementary particles mediating the electromagnetic interaction, can exhibit hadronic properties under specific conditions. This duality arises from a photon's quantum ability to fluctuate into a virtual quark-antiquark pair. At sufficiently high energies, these virtual quarks can become real particles by interacting with other hadrons, thereby imparting hadron-like characteristics to the photon.

This phenomenon, known as resolved photon processes, is observed when photons with energies exceeding a few GeV acquire a complex internal structure. In such cases, the photon no longer acts as a point-like particle but reveals its transient composition of quarks and gluons, as described by Quantum Chromodynamics (QCD). Resolved photon processes are crucial in electron-proton and electron-positron colliders, where they often dominate the production of hadronic final states, including collimated particle jets.

Understanding these processes is fundamental for particle physics, particularly in the context of future high-energy lepton colliders. The implications of the hadronic nature of photons for background generation in these experiments are not yet fully understood. Research in this area is vital for accurately interpreting experimental results and for the development of new theories describing fundamental interactions.