Load all images from a folder using PIL

See this answer, which uses PIL.Image and glob to find all images in the folder and load them into an array.

from PIL import Image
import glob
image_list = []
for filename in glob.glob('yourpath/*.gif'): #assuming gif
    im=Image.open(filename)
    image_list.append(im)

You'll need to specify a wildcard at the end of your path and iterate:

images = []
for f in glob.iglob("D:/Users/username/Desktop/cells/Marked/*"):
    images.append(np.asarray(Image.open(f)))

images = np.array(images)