First, as Ningauble has noted, the Brothers De Bry are not in the story save by the brief mention of their being the artists who did the plates for the Regnum Congo. They are not depicted in any way; no information is given on them whatsoever beyond that in the previous sentence. However, you may have an interesting point about the frequency with which mention of brothers -- whether they are actual characters in a tale or not -- and weird or unnatural happenings are connected in Lovecraft's work. It would be an interesting survey to see how often these occur.
People don't chop each other to pieces and eat human flesh for little or no reason. There has to be an influence.
Well, yes and no. Think of the various notorious cannibals of history. Think of Elizabeth Bathory, who bathed in the blood of virgins
because she thought it kept her young. Then there are simply those who are cannibals for other, personal reasons -- Jeffrey Dahmer and Ed Gein being prominent examples in recent American criminal history. As for there being an influence, as Ningauble has stated, the cannibal here gives his reasons plainly in the text:
"When I read in Scripter about slayin’—like them Midianites was slew—I kinder think things, but I ain’t got no picter of it. Here a body kin see all they is to it—I s’pose ’tis sinful, but ain’t we all born an’ livin’ in sin?—Thet feller bein’ chopped up gives me a tickle every time I look at ’im—I hev ta keep lookin’ at ’im—see whar the butcher cut off his feet? Thar’s his head on thet bench, with one arm side of it, an’ t’other arm’s on the graound side o’ the meat block.[...] Onct I tried suthin’ funny—here, young Sir, don’t git skeert—all I done was ter look at the picter afore I kilt the sheep for market—killin’ sheep was kinder more fun arter lookin’ at it—[...] Killin’ sheep was kinder more fun—but d’ye know, ’twan’t quite satisfyin’. Queer haow a cravin’ gits a holt on ye— As ye love the Almighty, young man, don’t tell nobody, but I swar ter Gawd thet picter begun ta make me hungry fer victuals I couldn’t raise nor buy—here, set still, what’s ailin’ ye?—I didn’t do nothin’, only I wondered haow ’twud be ef I did— They say meat makes blood an’ flesh, an’ gives ye new life, so I wondered ef ’twudn’t make a man live longer an’ longer ef ’twas more the same—”
This, too, ties into the Biblical quote "For the blood is the life" (Deut. 12:23; cf. Gen. 9:4 and Lev. 17:11) -- a quote also used in connection with Dracula, incidentally.
I believe that the picture had an influence on anyone who looked at it and the source that makes sense based on the book being about Africans, is their voodoo religion.
Again, voodoo as such is not an African religion; it is a syncretistic blending of pre-existing beliefs of various tribes and elements of Roman Catholicism given their own slant to blend with those beliefs. Combine this with the totemism of the snake, and various beliefs developed under the reign of slavery, and you end up with the amalgam which is voodoo. While it did become a practice in Africa (Dahomey, if I remember correctly) voodoo has always been at its strongest in the slave cultures of the West Indies and, to a slightly lesser degree, some parts of the American South, etc. There is mention of "Injuns" in the story, but it is in a passage where even the old man is commenting on the inaccuracies of the picture, whereas the "sort of dragon with the head of an alligator" is "a fabulous creature of the artist" -- i.e., a creation of the artist's imagination without reference to a real beast. The Africans being white was, as stated, a mistaken -- deliberately or otherwise --
depiction of the artist,
not the genuine state of the tribe depicted.
As for this being your explanation of the events of the tale... it's an interesting take, but I'm afraid not supported by the text, which gives a quite adequate explanation for the occurrence of the cannibalism, the fascination with the picture, the general perversion of the old man, and even the appearance of the blood. The religion of the American Indians doesn't enter into the tale at all, not even by implication.
As for the link you sent on the voodoo connection... again, this is simply quoting from the same site from which I linked the picture itself -- this is noted by the "hosted by Angelfire" at the top of the page -- and that site is, as you can see by reading the rest of the text, devoted to a Lovecraf-based game. The "facts" there are not to be trusted as genuine, but are rather concocted of part actual historical fact and large amounts of pure fiction, for the purposes of enhancing the atmosphere of the game's scenario.
The problem with what you are bringing in here, though it is as I said an interesting interpretation, is that it isn't supported by the text of Lovecraft's tale, nor by things in his other stories -- such as, for example, George Wetzel's idea of the "ghoul-changeling", which is a theme Lovecraft developed through several stories, from a nascent, inchoate form such as we may see here (though this is arguable) to the final overt statement of such in "Pickman's Model". That is the risk of bringing too much of one's own views to the reading of a tale: you end up
imposing a reading on a text which really can't be found in the text itself (even in relation to other texts by the same author), rather than
developing or
explicating something which is inherent at some level in the original work.
(I repeat, though, that your idea concerning his use of brothers may be a quite valid one; at any rate, it is certainly worthy of examination.)
And, again, the blood in both tales is amply explained. In both cases, it is used to "[make] blood an’ flesh, an’ [give] new life"; here, by the cannibalistic hermit; there, for both Wilbur and his brother, whose ancestry is at least half alien, the father being Yog-Sothoth.....
