Image Processing: Isolating areas of an image with internal irregularity

Question

I am trying to isolate each of the blue painted fingernails in the image. However, I am not sure what approach should be considered due to the white design on each nail interrupting the otherwise uniform nail color. This of course, makes EdgeDetect a lot harder to apply. Any suggestion would be appreciated.

i = Import["https://i.stack.imgur.com/46JAy.jpg"]

+++++++++++++++++++++++++++++++++ UPDATE +++++++++++++++++++++++++++++++++++++

Thanks to both Belisarius and Vitaliy Kaurov for your in depth responses. I am trying to consider a more general case such as the following image. I would like to use an edge detection approach to find the area of the nails. using a MedianFilter does help a lot and isolates the nail areas. However, what would be the next step in using the result to detect the nail areas? I am guessing that I would need to 'complete' the circles of these lines first. Is there a better approach? Perhaps measuring the density of the lines would be the best...

i = Import["https://i.stack.imgur.com/6khSE.png"]

EdgeDetect[MedianFilter[i, 4]]

Answer 1

i = Import["https://i.stack.imgur.com/46JAy.jpg"]
(*Let's first find the blue zone*)
(*Separate Colours and negate*)
{rr, gg, bb} = ColorNegate /@ ColorSeparate@i

(*Increase contrast*)
msf = MeanShiftFilter[ImageMultiply[ImageMultiply[ColorNegate@bb, rr], gg], 2, .1]

(*Binarize and delete small dots*)
blueMoon = DeleteSmallComponents[Binarize[msf], 10]

(*Now Find zigzags*)
zigs = Binarize[ColorNegate@gg, .99]  

(*Add zigs to moons and eat up dots*)
c = Erosion[Dilation[ImageAdd[zigs, blueMoon], 10], 10]

We are done. Let's play a bit with the results

(*Colorize and count the fingers: 5. Another boring human being*)
(*I bet her hair is green and she has a snake tatooed down there*)
Colorize[MorphologicalComponents[c], ColorFunction -> "BrightBands"]

(*See what we found*)
ImageMultiply[c, i]

No tatoo :(

Answer 2

It all depends on what you mean by "isolate". Here is a start. I will use function called ClusteringComponents which finds clusters of pixels with similar values in image. We have quite a few different type of elements: skin, nails, zigzag line, a few background elements. Some have a bit close nature - like whitish-yellowish color of zigzags and the skin. So you have to specify large enough number of clusters to pick all those up, but not too big to make later search through them cumbersome. "Make everything as simple as possible, but not simpler." ~ Albert Einstein - a typical optimization statement ;-) For example, choosing number of clusters to be 8 will not be able to distinguish between zigzags and part of the skin:

i = Import["https://i.stack.imgur.com/46JAy.jpg"];
x = ClusteringComponents[i, 8] ; x // Colorize

But 9 clusters already will do:

x = ClusteringComponents[i, 9]; ArrayPlot[x]

From this image we see that in the array (matrix) x produced by ClusteringComponents nails and zigzags are the darkest, so they got the highest index values. Because we had 9 clusters, this line is obvious:

ArrayPlot[x, ColorRules -> {9 -> Red, 8 -> Blue}, FrameTicks -> True]

You can also completely remove the background:

ArrayPlot[x, ColorRules -> {9 -> Red, 8 -> Blue, _ -> White}, FrameTicks -> True]

And finally you can find all sorts of things, like where the centers of nails are and what is the radius of an equivalent disk:

Show[i, Graphics[{Red, Thickness[.01], Circle[#[[1]], #[[2]]] & /@ 
    ComponentMeasurements[DeleteSmallComponents[Dilation[
        Image[x /. (# -> 0 & /@ Range[7])~Join~{8 -> 1, 9 -> 1}], 
        3]], {"Centroid", "EquivalentDiskRadius"}][[All, 2]]}]]