I believe these questions should be considered off-topic if the gist of the plant identification question is "is this edible?".
Because we're food specialists and not necessarily plant specialists, it's completely possible for us to miss-identify something as "edible" that is not.
As in the question, it's possible that it's a perfectly edible peppermint... but it's also possible that it's poisonous... and, honestly, even a plant specialist would probably be hesitant to attempt to identify which exact species of mint a plant is from an image.
We already have a policy of "when in doubt, throw it out" and we don't generally answer specific "is this safe to eat" questions, instead opting to close them as duplicates of the master question I linked here.
I feel that this type of "is this edible" question could fall into a related category where our policy is to either
Create a master question that discourages consumption of plants that are of unknown species and to close new questions as a duplicate of this master question.
Migrate the questions to the more knowledgeable plant experts over at Gardening.SE who can, hopefully, tell them the likelihood of it being safe to eat.
That being said, if the person purchased or was given the item as food, as in this question (Help Identifying a pale green, spherical squash-y like vegetable) which came from a farmer's market, this isn't a safety issue, it's more generally an attempt to figure out what they have so they can find out how best to prepare it.
I found an older Meta question with a different initial question but a similar conclusion:
Questions about foraging
Questions strictly about identifying wild foods, like this one, are more than likely off-topic because they usually can't be narrowly answered.
However, not all questions about wild foods are the same. For example this question about when to pick blueberries could be considered a "foraging question," but assuming the food item has already been properly identified, the subsequent answer ensures that the ingredients used are in their proper state before cooking.