Extension for creating dependent custom fields?

I’m wondering if anyone has come across (or dreamed of) an extension that allows you to specify cascading or dependent custom fields.

For instance, say I have the following fields:

• Image
• Textarea
• Link

When using the publish form, I only want “Link” to appear if I upload an image. Otherwise, it should stay hidden. Textarea should always appear, as normal.

The logic would go something like:

IF user uploads in image THEN allow the user to specify a link

• or -

IF the Image custom field is defined THEN display the Link custom field

Possible?