I only recently found this puzzle and thought I might spend a little time thinking about it. I went through every page of this (painful) thread to see if my own thoughts on the puzzle had been stated by anyone else, and it seems I might have some original ideas. As much as I would like to have the "Eureka!" moment and sweep the private key for myself, I thought it would be better to share.

My thoughts/findings are not listed in any particular order of priority:

• I do not see a rabbit. There may be hidden imagery, but I do not believe that the rabbit so many people are talking about is of any substance.
• I have read a lot of people looking at the "flame" border as a potential binary message. Rather than the height or width of each flame, it makes more sense to me that the color would indicate each bit. What sticks out to me the most is the red-bordered flames. Each of these red bordered flames is filled with either green or purple(blue/violet depending on the color depth of your screen). My thought was that maybe it could be that green=1 and purple=0 or vice-versa.
• Following my original thought that the red flames are the message, I have also considered that the inner and outer rows of flames in the border might each represent 0 an 1, respectively (or vice-versa). I have also seen a reference to http://yewknee.com/blog/peter-saville-colour-code/ which seemed like it might be something worth exploring.
• The glyphs in each of the corners look like Ulam spirals to me. Ulam spirals are used to represent prime numbers. If these are Ulam spirals, then they would each have a value of 17. This caught my attention as it matches the 17 leaves in the painting.
• Whether or not the glyphs are Ulam spirals, I agree that they might also indicate a direction to read the information in the image. Not just the border, however. I think they might indicate how to read the symbols/objects in the middle of the painting as well. One way that I approached this was to examine the chess board in 5x5 "quadrants"
   at each corner, then trace the path of the glyphs through squares contained within each quadrant. If these are all drawn on the board at the same time there is overlap, but I am not sure if that matters. Hell, I am not sure of anything. Example here: https://imgur.com/a/v1EoS
• I looked at the *.tif in a hex editor and I found the string "bitcoin mystery 076".
• I have seen a number of posts where people "zoom and enhance" sections to find characters or hidden imagery. It is obvious that this was done with paint, perhaps acrylic. There may have been other mediums incorporated as well, or other tools besides paint brushes. There are portions that do look like she used the back of her brush handle or another hard instrument. In my experience with paint, especially when applied as liberal this appears to have been, intentionally adding in the tiny details would be more obvious. I think a lot of the details and hidden images people are seeing can be chalked up to artifacts created by brush strokes and color blending/bleeding.
• Do we know how large the painting is in physical dimensions? Knowing the physical dimensions might give us a better idea of the level of detail to look for. The *.tif is 24"x18".
• Maybe this whole thing is much more simple than we expect. I am entertaining the possibility that each of the objects might represent a character or series of characters. For example, the black knight/horse could be BK, bk, Bk, bK, k, K, or any of those with "h" instead of "k". Following that logic, maybe the number of flames of certain color might be something worth examining (example, if there are 16 red flames with purple fill, it might be 16rp or something like that).
• Maybe rather than looking for a private key in its entirety, we should be looking for the variables required to calculate the private private key (base point, prime modulo,
   etc.). I am not as well-versed in the math as I would like to be, so perhaps someone who is could chime in.

Anyway, I just wanted to list out my own thoughts and see if this might light a fuse of inspiration for anyone.