[bug] fast_image_processor register error
Author: JJJYmmm
Pull request: no
Labels: name: bug

### System Info

- `transformers` version: 4.50.0.dev0
- Platform: Linux-5.15.0-119-generic-x86_64-with-glibc2.35
- Python version: 3.10.16
- Huggingface_hub version: 0.29.3
- Safetensors version: 0.5.3
- Accelerate version: 1.2.1
- Accelerate config:    not found
- DeepSpeed version: not installed
- PyTorch version (GPU?): 2.6.0+cu124 (True)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using distributed or parallel set-up in script?: <fill in>
- Using GPU in script?: <fill in>
- GPU type: NVIDIA A100-SXM4-80GB

### Who can help?

_No response_

### Information

- [ ] The official example scripts
- [x] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

Hi!😊 @Rocketknight1 

I've encountered a bug while registering a fast image processor. Below is the reproduction code snippet:

```python
from transformers import AutoImageProcessor
from transformers.models.qwen2_vl import Qwen2VLConfig, Qwen2VLImageProcessorFast

class NewVLProcessor(Qwen2VLConfig):
    pass

class NewImageProcessorFast(Qwen2VLImageProcessorFast):
    pass

AutoImageProcessor.register(NewVLProcessor, fast_image_processor_class=NewImageProcessorFast)
```

During registration, the following error was raised:

```
File "/home/test/anaconda3/envs/human/lib/python3.10/site-packages/transformers/models/auto/image_processing_auto.py", line 607, in register
    raise ValueError("You passed a slow image processor in as the `fast_image_processor_class`.")
ValueError: You passed a slow image processor in as the `fast_image_processor_class`.
```

`NewImageProcessorFast` is a subclass of `BaseImageProcessorFast`, which qualifies it as a fast image processor. However, since `BaseImageProcessorFast` itself inherits from `BaseImageProcessor`, the following condition evaluates to true, triggering an error:

```python
# transformers/models/auto/image_processing_auto.py, line 607
if fast_image_processor_class is not None and issubclass(fast_image_processor_class, BaseImageProcessor):
    raise ValueError("You passed a slow image processor in as the `fast_image_processor_class`.")
```

I think the following quick fix should resolve the issue by ensuring that only classes inheriting from `BaseImageProcessorFast` are considered fast image processors:

```python
if fast_image_processor_class is not None and not issubclass(fast_image_processor_class, BaseImageProcessorFast):
    raise ValueError("You passed a slow image processor in as the `fast_image_processor_class`.")
```

### Expected behavior

Register successfully

Comments:
cc @zucchini-nlp @yonigozlan 

Though also note that #36184 should be merged very soon and might help with this!

Hi @JJJYmmm, thanks for flagging this ! I agree with your modifications, although we might want to change the error message to something like "The `fast_image_processor_class` should inherit from `BaseImageProcessorFast`."

@yonigozlan OK! Let's change the error message to 
```python
ValueError("The `fast_image_processor_class` should inherit from `BaseImageProcessorFast`.")
```