Face recognition uses principal component analysis (PCA) to reduce the dimensionality of face image data and identify patterns to recognize individuals. PCA involves extracting principal components from the data to summarize it with fewer variables while highlighting similarities and differences. The process involves getting sample face image data, subtracting the mean, calculating the covariance matrix, finding eigenvectors and eigenvalues to form a feature vector for projections of the data in the direction of the principal components. This allows for face recognition by training a database and testing unknown images.