KeyError: dataset has no key "image"
### Describe the bug

I've loaded a local image dataset with:
`ds = laod_dataset("imagefolder", data_dir=path-to-data)`

And defined a transform to process the data, following the Datasets docs.

However, I get a keyError error, indicating there's no "image" key in my dataset. When I printed out the example_batch sent to the transformation function, it shows only the labels are being sent to the function.
For some reason, the images are not in the example batches.

### Steps to reproduce the bug

I'm using the latest stable version of datasets 

### Expected behavior

I expect the example_batches to contain both images and labels

### Environment info

I'm using the latest stable version of datasets 