Labeling images using own trained classifier

try like this:

newImage = imread(fullfile(rootFolder, 'airplanes', 'image_0690.jpg'));

% Create augmentedImageDatastore to automatically resize the image when
% image features are extracted using activations.
ds = augmentedImageDatastore(imageSize, newImage, 'ColorPreprocessing', 'gray2rgb');

% Extract image features using the CNN
imageFeatures = activations(net, ds, featureLayer, 'OutputAs', 'columns');

% Make a prediction using the classifier
label = predict(classifier, imageFeatures, 'ObservationsIn', 'columns')