No, it is not possible to set an initial value for a <input type="file" />
element. The reason for this constraint (which is enforced by the browser, not by ASP.NET) is security. Consider the consequences of a malicious website owner placing the following in a form:
<input type="file" value="c:\bank\secret.key" />
However, I am not sure that this limitation is really a problem in the scenario you are describing. Having the <input type="file">
prefilled with the path to the image file on the server, is unlikely to help anyway, as the value selected in a file field is used to point to a file on the client, which will be uploaded as part of the form postback.
Instead, consider constructing your edit form in a way where the current image is displayed (possibly as a thumbnail) along with an <input type="file">
field for uploading a new image to overwrite the existing, and a checkbox allowing the user to remove the current image (if this action is allowed).