Add photos to separate folders for each class.
In the case of this code https://github.com/pjablonski123/alk_eye-tech/blob/master/eva_3_4c_dss.ipynb there were 4 folders with the following names:
classes = ['CNV', 'DME', 'DRUSEN', 'NORMAL']
The name of the folder is the name of the class. They were placed in each train and test folders:
train_dir = '/content/drive/My Drive/TEST1/'
test_dir = '/content/drive/My Drive/TEST2/'
The code read pictures from the folders and classes automatically.