Comment 3 for bug 410972

xml2po already does that in a succint way:

#. When image changes, this message will be marked fuzzy or untranslated for you.
#. It doesn't matter what you translate it to: it's not used at all.
#: C/accerciser.xml:461(None)
msgid "@@image: 'figures/script_recorder.png'; md5=a15027c852c58df789886f6aadf0130c"
msgstr ""

#: C/accerciser.xml:24(title)
msgid "<application>Accerciser</application> Manual v0.2.0"
msgstr ""

#: C/accerciser.xml:27(year)
msgid "2006"
msgstr ""

Notice that in a specific situation a more verbose comment was added. This could apply also for strftime-formated messages, or messages with placeholders in general, as well as messages with old-style or new-style context.