Here's my idea, though i'm not patient enough to run all the variations
There flames are actually coded in 16 combinations
Yellow
Red
Purple (could be blue my screen is weird)
Green
Tall
Short
Line inside
Fill Inside
so one flame for example = YPLS Yellow/Purple Line Short,
thus here all all the combinations
YPLS
YPFS
YPLT
YPFT
YGFS
YGLT
YGLS
YGFT
RPLT
RPFT
RPFS
RPLS
RGFT
RGFS * appears once only hmm
RGLT
RGLS
so each set of parameters could be a baconion cypher, or the flames themselves could be individual letters or numbers, Ucase lcase etc.
On another note, if i zoom in in photoshop on the strange white uneven border, and adjust my levels high, i see some patterns in the noise of the white border, could be just a jpeg artifiact, but figured i'd show you. Here's just a small cropping from the upperleft corner of the image
http://imgur.com/WTTieOB3rd idea, if we want to get really crazy, is that she actually wrote all the characters on the painting. I see FO on the dove, an L and d on the Phoenix, a large black C in the darkest black square and possibly a 3 on the bottom of the queen inside the red triangle.....
I like your idea, but I'm having trouble looking for the line inside the flame. How many line inside flames are there?
I think a Hex format of the private key is best because of the 16 combinations you found. We can label each unique flame with a hex character. I don't know why there are more than 64 flames which is the number of chars in a hex private key
YPLS 0
YPFS 1
YPLT 2
YPFT 3
YGFS 4
YGLT 5
YGLS 6
YGFT 7
RPLT 8
RPFT 9
RPFS A
RPLS B
RGFT C
RGFS D
RGLT E
RGLS F