# callbacks.onImageRequest

Part of [Callbacks](https://kernstra.com/docs/web-sdk/config/callbacks) in the Kernstra Web SDK 1.0.0 configuration reference.

- Type: `() => Promise<Blob | null>`
- Page: https://kernstra.com/docs/web-sdk/config/callbacks/onimagerequest

Replaces the Image tool's picker: called when the Image tool would open its file picker. Resolve with a `Blob` (a `File` is one) or `null` to cancel; the image is checked against [`tools.image`](https://kernstra.com/docs/web-sdk/config/tools/image) like a picked file and refused with the same message. A rejection is a cancel and is logged; the SDK shows nothing for a cancel, so tell the user yourself if your flow failed. An answer that arrives after the tool was switched off is dropped.

Web page: https://kernstra.com/docs/web-sdk/config/callbacks/onimagerequest