title: cv2.imread does not read jpg files
body: <p>I am working on a toolbox in Python where I use <code>cv2.imread</code> function to load images. </p>
  
  <p>While I am working with <code>.png</code> files it is OK, but it returns <code>NoneType</code> when I want to read a <code>.jpg</code> file from the same folder.</p>
  
  <ol>
  <li>Why does this happen? and how can I fix it?</li>
  <li>How can I read images from a subfolder?</li>
  </ol>
  
  <p>Thanks</p>
  
  <pre><code>import sys
  import numpy as np
  import os
  sys.path.append("/usr/local/lib1/python2.7/site-packages")
  import cv2
  im1=cv2.imread('pic1.png')
  print im1.shape
  #output: (512, 512, 3)
  im2=cv2.imread('pic1.jpg')
  print im2.shape
  #output:
  -------------------------------------------------------------------------
  AttributeError                         Traceback (most recent call last)
  &lt;ipython-input-8-2d36ac00eca0&gt; in &lt;module&gt;()
  ----&gt; 1 print im2.shape
  AttributeError: 'NoneType' object has no attribute 'shape'
  
  
  print cv2.getBuildInformation()
  
  Media I/O: 
  ZLib:                        /lib64/libz.so (ver 1.2.8)
  JPEG:                        /lib64/libjpeg.so (ver 80)
  WEBP:                        /lib64/libwebp.so (ver encoder: 0x0202)
  PNG:                         /lib64/libpng.so (ver 1.6.17)
  TIFF:                        /lib64/libtiff.so (ver 42 - 4.0.2)
  JPEG 2000:                   /lib64/libjasper.so (ver 1.900.1)
  </code></pre>
  
  <p>Two pictures are in my home folder:</p>
  
  <p><a href="https://i.stack.imgur.com/i2IDX.png" rel="noreferrer"><img src="https://i.stack.imgur.com/i2IDX.png" alt="enter image description here"></a></p>
  
  <pre><code>  from os import getcwd, listdir, path
    current_dir = getcwd()
    files = [f for f in listdir('.') if path.isfile(f)]
    print(('Current directory: {c_dir}\n\n'
           'Items in the current directory:\n   {files}').format(
           c_dir=current_dir, 
           files=str.join('\n   ', files)))
    #Output:
    Items in the current directory:
    .node_repl_history
    mysh.sh~
    test.sh
    blender_tofile.sh
    **pic1.jpg**
    rapid.sh
    matlab_crash_dump.8294-1
    .gtk-bookmarks
    any2any
    beethoven.ply
    Face.blend
    Untitled1.ipynb
    sphere1.pbrt
    multirow.log
    .Xauthority
    .gtkrc-2.0-kde4
    Theory and Practice.pdf
    simple_example.gpx~
    pbrt.sh
    blender.sh~
    Untitled4.ipynb
    java.log.3414
    kinect_test.py
    matlab_crash_dump.7226-1
   .bashrc~~
   .ICEauthority
   infoslipsviewer.desktop
   GTW_Global_Numbers.pdf
   index.htm
   Untitled2.ipynb
   **pic1.png**
  
  
  
   os.access('pic1.jpg', os.R_OK)
   #output:
   True
  </code></pre>