上传头像的报错信息

Traceback (most recent call last):
File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 513, in __call__
handler.post(*groups)
File "/base/data/home/apps/v2ex/1.341787447319303929/member.py", line 280, in post
avatar_73 = images.resize(avatar, 73, 73)
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/images/__init__.py", line 625, in resize
return image.execute_transforms(output_encoding=output_encoding)
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/images/__init__.py", line 523, in execute_transforms
raise BadImageError()
BadImageError