The forum guidelines recommend using magiccards.info for card images. This results in something like this:
However, magiccards.info was discontinued and absorbed into scryfall sometime between m19 and c18. While scryfall handles the old magiccards.info image linking, they have their own image formatting going on and have not bothered updating the magiccards.info resource with new cards. There's a stylistic analog to the old magiccards.info one, but it's considerably bigger, making adding post-m19 cards to magiccards.info formatted threads visually incoherent.
The easiest way around this would be to enable image resizing in the img bbcode tag. This makes the system future-proof to some degree - shall the standard shift again going forward, this should make it easy to keep thread formatting consistent. Hope this isn't too much hassle. The magiccards.info card size was perfect for this particular forum, offering a great balance of legibility and real estate use.