预训练模型下载：
ch_PP-OCRv4_det_server_train：https://paddleocr.bj.bcebos.com/PP-OCRv4/chinese/ch_PP-OCRv4_det_server_train.tar
ch_PP-OCRv4_rec_server_train：https://paddleocr.bj.bcebos.com/PP-OCRv4/chinese/ch_PP-OCRv4_rec_server_train.tar
ch_ppocr_server_v2.0_det_train：https://paddleocr.bj.bcebos.com/dygraph_v2.0/ch/ch_ppocr_server_v2.0_det_train.tar
ch_ppocr_server_v2.0_rec_train：https://paddleocr.bj.bcebos.com/dygraph_v2.0/ch/ch_ppocr_server_v2.0_rec_train.tar