how to predict my own image using cnn in keras after training on MNIST dataset

I have made a convolutional neural network to predict handwritten digits using MNIST dataset but now I am stuck at predicting my own image as input to cnn,I have saved weights after training cnn and want to use that to predict my own image (NOTE : care is taken that my input image is 28×28)

code:

new_mnist.py :

ap = argparse.ArgumentParser()
ap.add_argument("-s", "--save-model", type=int, default=-1,
help="(optional) whether or not model should be saved to disk")  
ap.add_argument("-l", "--load-model", type=int, default=-1,
help="(optional) whether or not pre-trained model should be loaded")
ap.add_argument("-w", "--weights", type=str,
help="(optional) path to weights file")
args  = vars(ap.parse_args())

# fix random seed for reproducibility
seed = 7
numpy.random.seed(seed)

# load data
print("[INFO] downloading data...")
(X_train, y_train), (X_test, y_test) = mnist.load_data()
# reshape to be [samples][pixels][width][height]
X_train = X_train.reshape(X_train.shape[0], 1, 28, 28).astype('float32')
X_test = X_test.reshape(X_test.shape[0], 1, 28, 28).astype('float32')
print(X_test.shape[0])

# normalize inputs from 0-255 to 0-1
X_train = X_train / 255
X_test = X_test / 255
# one hot encode outputs
y_train = np_utils.to_categorical(y_train)
y_test = np_utils.to_categorical(y_test)
num_classes = y_test.shape[1]

# build the model
print("[INFO] compiling model...")
model = LeNet.build(num_classes = num_classes,weightsPath = args["weights"]          if args["load_model"] > 0 else None)
model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])

if args["load_model"] < 0:
# Fit the model
print("[INFO] training...")
model.fit(X_train, y_train, validation_data=(X_test, y_test), epochs=1,    batch_size=200, verbose=2)
# Final evaluation of the model
print("[INFO] evaluating...")
scores = model.evaluate(X_test, y_test, verbose=0)
print("Baseline Error: %.2f%%" % (100-scores[1]*100))
elif args["load_model"] > 0:
im = imread("C:\Users\Divyesh\Desktop\mnist.png")
im = im/255
pr = model.predict_classes(im)
print(pr)

# check to see if the model should be saved to file
if args["save_model"] > 0:
print("[INFO] dumping weights to file...")
model.save_weights(args["weights"], overwrite=True)

lenet.py :

class LeNet:
@staticmethod
def build(num_classes,weightsPath = None):
# create model
    model = Sequential()
    model.add(Convolution2D(30, 5, 5, border_mode='valid', input_shape=(1, 28, 28), activation='relu'))
    model.add(MaxPooling2D(pool_size=(2, 2)))
    model.add(Convolution2D(15, 3, 3, activation='relu'))
    model.add(MaxPooling2D(pool_size=(2, 2)))
    model.add(Dropout(0.2))
    model.add(Flatten())
    model.add(Dense(128, activation='relu'))
    model.add(Dense(50, activation='relu'))
    model.add(Dense(num_classes, activation='softmax'))
    # Compile model
    #model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])
    if weightsPath is not None:
        model.load_weights(weightsPath)
    return model

in new_mnist.py I have called predict(im) in which im is 28×28 image but after running this program I get error as:

ValueError: Error when checking : expected conv2d_1_input to have 4      dimensions, but got array with shape (28, 28)

HELP!!!