ImageData_999.csv
ImageData_1000.csv

ImageData_3259
ImageData_3289
ImageData_811
ImageData_907

ImageData_811
ImageData_907
ImageData_3259
ImageData_3289

for root, dirs, files in os.walk(path):
    for file in fnmatch.filter(files, filter):
        yield os.path.join(root, file)