[racket] Is Scribble supposed to overwrite old image files during rendering?

We're using Scribble with the "--dest" output flag; when we apply
scribble individually on files that have images into the same
destination directory, the autogenerated image names can collide.  For
example, the names 'pict.png' and 'pict_2.png' can easily collide.

Does anyone have suggested workarounds?  It might be nice to put a
prefix on the names of the files so that there's no collision nor
inadvertent image overwrite.


(Alternatively, I suppose I can probably call into the html-renderer
directly, without going through the command line utility.  That way,
whatever hidden state is being used to create fresh names continues to
be fresh.  But if there's something I can do from the command line
utility, that'd be great.)

Thanks!