Board Thread:Support Requests - Getting Technical/@comment-301511-20190315001538/@comment-24155515-20190315170800

Just specify the "default" tag within the image tag in the infobox source code, as noted here. It's built into the functionality, AFAIK.

So, like:

File:Placeholder

That should work? Without my testing it?

(EDIT: Shoot, no. I misunderstood the question. (I thought it was a "how do I specify that as a default input for the parameter".) Ignore me. But I'll not delete it in case anyone else misunderstood the question in the exact same way I did, so they have an answer if they were looking for one.

P.S. I tested my solution to see if it'd work with File:Placeholder anyway. It does not.)