Pictures still speak the most universally understood language. (Walt Disney)
My constituents don't know how to read, but they can't help seeing them damned pictures. (Boss Tweed)
Here are three examples from classic D&D where the raw text said one thing, and the picture or table presented a special-case or variant way of doing it. In each case, I think that everyone I know remembers the picture, and mis-remembers the actual core rule from the text itself.
OD&D Monster Reactions
The OD&D text says this:
Monsters will automatically attack and/or pursue any characters they "see", with the exception of those monsters which are intelligent enough to avoid an obviously superior force. [OD&D Vol-3, p. 12]Further down on that page, there is expansion on this "exception" to intelligent monster reactions, in table form:
2-5 negative reactionNow, keep in mind that this table was supposed to be the "exception" for "more intelligent monsters". Presumably that's got to be a small minority of monsters -- in my reading, not just quasi-human intelligence like orcs and goblins, but special mastermind-level monsters like wizards, medusae, and vampires. And even then it was supposed to be applicable only in the face of an "obviously superior force". But generally folks forget about the original core rule (i.e., "automatically attack") and focus solely on the table.
6-8 uncertain reaction
9-12 positive reaction
In later editions, the reaction table was copied forward, but the default rule text was abandoned. The idea of a "random reaction table" became so universal that it was the very first thing the makers of Futurama thought to have the Gygax character do upon his introduction.
AD&D Combat Progression
In an apparent change from OD&D, AD&D inserts a sequence of 6 "20"'s in the combat tables before a value of "21" is reached. The DMG notes:
A quick glance at the progression of numbers on the COMBAT TABLES will reveal that 20 is repeated. This reflects the fact that a 20 indicates a "perfect" hit. It also incidentally helps to assure that opponents with high armor class value are not "hit proof" in most cases. [AD&D 1E DMG, p. 82]Notice what this does not say: there's no special treatment of those 20's, no special way of calculating the attack total, no discounting of bonuses or magic. That comes later:
Should any DM find that this system offends his or her sensibilities, the following modification is suggested: Consider the repeated 20 as a perfectly-aimed attack which does not gain any benefit from strength or magical properties of any sort - spell, missile, or weapon. That is, the 20 must be attained by a roll of natural 20... Thus, the COMBAT TABLES could be amended to read like this:Again, lots of people overlook the fact that the AD&D core rule allows you to hit any "20" (or more) by any means that you can add up the numbers, including bonuses and magic. What folks remember is this modified/"amended" table with its stipulation of "20 (natural)" in most of the cases. And that's the kind of thing that got translated to later editions as the "natural 20 always hits" rule.
AD&D Random Dungeon Generation
The back of the DMG has a nifty section titled "Appendix A: Random Dungeon Generation". Among the introductory paragraphs, it says this:
The first level of the dungeon is always begun with a room; that is, the stairway down leads to a room, so you might go immediately to TABLE V. and follow the procedure indicated or use one of the following "starter" areas. Always begin a level in the middle of the sheet of graph paper. [AD&D 1E DMG, p. 169]So notice what the primary rule is: "go immediately to TABLE V" (i.e., a list of different chamber/room sizes, from 10'×10' to 30'×40' or more). Or, here is the secondary possibility, the pregenerated "starter" areas:
As you might guess, because it comes in highly-memorable visual form (and assisted by the non-qualified title in the figure), I think that most people wind up using these "starter" areas over and over again, repetitively starting random dungeons with these same recognizable shapes, even when the core rule is actually to do something different (namely, go to Table V. and roll a random probably-rectangular room).
So in conclusion: Only use a picture or table when you really want that element to be highly memorable. Probably you don't want to use an illustration for a variant that's at odds with a core rule communicated solely by text! For clarity I present this point in picture form: