File “/py-faster-rcnn/tools/../lib/datasets/imdb.py”, line 108, in append_flipped_images 
assert (boxes[:, 2] >= boxes[:, 0]).all() 
AssertionError

问题解决：

1、修改lib/datasets/imdb.py，append_flipped_images()函数,在一行代码为 boxes[:, 2] = widths[i] - oldx1 - 1下加入代码：

for b in range(len(boxes)):
  if boxes[b][2]< boxes[b][0]:
    boxes[b][0] = 0

	将对Xmin,Ymin,Xmax,Ymax减一去掉
将对Xmin,Ymin,Xmax,Ymax减一去掉

3、（可选，如果1和2可以解决问题，就没必要用3）修改lib/fast_rcnn/config.py，不使图片实现翻转，如下改为

# Use horizontally-flipped images during training?
__C.TRAIN.USE_FLIPPED = False