She later said in a separate post: “You don’t scare me, Giorgia Meloni. After all, you’re only 1.2m [3ft 9in] tall. I can’t even see you.”
Ms Meloni’s height is reported in Italian media to be 1.63m (5ft 3in).
Ms Cortese was cleared for posting the initial image but convicted over the later tweets.
She has the option to appeal but has not yet confirmed whether she will do so.
Ms Meloni’s lawyer said she would donate any money she received to charity.
Responding to the verdict on X, Ms Cortese wrote: “Italy’s government has a serious problem with freedom of expression and journalistic dissent.
“This country seems to get closer to [Viktor] Orbán’s Hungary: these are bad times for independent journalists and opinion leaders. Let’s hope for better days ahead. We won’t give up!”
She later added that she was “Italian and proud to be” but that “we deserve better than this appalling and shameful government”.