Hi!

While working on Reproducible Builds for Tails, we noticed that
the img plugin's output is not deterministic: PNG images embed
timestamps.

The `img-determinism` branch in the
`https://git-tails.immerda.ch/ikiwiki.git` Git repository has a fix
for this problem + a new test (that fails without this change, and
succeeds with the branch merged).

--[[intrigeri]]

> Thanks, [[merged|done]] --[[smcv]]

[[!tag patch]]
