Data augmentation
Data augmentation is a very important technique to improve classification accuracy. Data augmentation consists of creating new samples from existing samples, by adding some jitters such as:
Random scale
Random sized crop
Horizontal flip
Random rotation
Lighting noise
Brightness jittering
Saturation jittering
Contrast jittering
This will help the model to be more robust to different lighting conditions that are very common in real life.
Instead of always seeing the same dataset, the model discovers different samples at each epoch.
Note that input normalization is also important to get better results.