OpenCV Error: Assertion failed (_img.rows * _img.cols == vecSize)
I solved it haha.  Even though I specified in the command the width and height to be 20x20, it changed it to 20x24.  So the opencv_traincascade command was throwing an error.  Once I changed the width and height arguments in the opencv_traincascade command it worked.
I keep getting this error
OpenCV Error: Assertion failed (_img.rows * _img.cols == vecSize) in get, file /build/opencv-SviWsf/opencv-2.4.9.1+dfsg/apps/traincascade/imagestorage.cpp, line 157
terminate called after throwing an instance of 'cv::Exception'
  what():  /build/opencv-SviWsf/opencv-2.4.9.1+dfsg/apps/traincascade/imagestorage.cpp:157: error: (-215) _img.rows * _img.cols == vecSize in function get
Aborted (core dumped)
when running opencv_traincascade.  I run with these arguments: opencv_traincascade -data data -vec positives.vec -bg bg.txt -numPos 1600 -numNeg 800 -numStages 10 -w 20 -h 20.  

My project build is as follows: 
workspace
|__bg.txt
|__data/ # where I plan to put cascade
|__info/
      |__ # all samples
      |__info.lst
|__jersey5050.jpg
|__neg/
   |__ # neg images
|__opencv/
|__positives.vec


before I ran opencv_createsamples -img jersey5050.jpg -bg bg.txt -info info/info.lst -maxxangle 0.5 - maxyangle 0.5 -maxzangle 0.5 -num 1800

Not quite sure why I'm getting this error.  The images are all converted to greyscale as well.  The neg's are sized at 100x100 and jersey5050.jpg is sized at 50x50.  I saw someone had a the same error on the OpenCV forums and someone suggested deleting the backup .xml files that are created b OpenCV in case the training is "interrupted".  I deleted those and nothing.  Please help! I'm using python 3 on mac.  I'm also running these commands on an ubuntu server from digitalocean with 2GB of ram but I don't think that's part of the problem.
EDIT
Forgot to mention, after the opencv_createsamples command, i then ran opencv_createsamples -info info/info.lst -num 1800 -w 20 -h20 -vec positives.vec