I think "Bromide" here means a kind of photographic print.
The only sources I've been able to find are a few instances in the British National Corpus. In a source identified as "[Miscellaneous articles about desk-top Pub]. Budget, Henry and et al. u.p., n.d., pp. ??. 4427 s-units." (1985-1998) there are the following:
supplied a typeset bromide and quoted 20 ex delivery for the job.
While all the other samples were clean edged both of those from The Setting Studio were torn off larger pieces of bromide. If we had actually wanted to use them we would have had to do some tidying as the area of the bromide was somewhat less than A4.
Bromide # a photographic print made on bromide paper.
The only disadvantage in moving across is the fact that you need to process the resulting film or bromide photographically
And in another source, identified as "[RAFA journal and miscellaneous info]. u.p., n.d., pp. ??. 1811 s-units." (no date), we see
Please supply final film/artwork in the following format: # Positive Film # Negative Film # Bromide (Please tick one box)
At first sight, this interpretation doesn't seem to make much sense, but if you read it in the context of other nearby "steps":
Will there be an additional charge for
complex layout?
e.g. multiple font changes, complex
tables…
Will there be an additional charge for
unusual difficulties?
e.g. poorly legible text, contact with
foreign informants…
I'm pretty sure that this is what it means. (Note that this is a British document).