How can I remove the white space within a cloud in TikZ?

I am trying to produce a figure which contains a cloud drawn around a set of images. The code I have so far is:

\node [draw, cloud, cloud puffs=20, aspect=2, inner sep=0cm] (pathways)
{\begin{tikzpicture}
\node at (0,0) [inner sep = 0pt] (pathway) {\includegraphics[width=5cm]{png/WP716_74442.png}};
\node at (2,1) [inner sep = 0pt] (pathway2) {\includegraphics[width=4cm]{png/WP716_74442.png}};
\node at (1,2) [inner sep = 0pt] (pathway3) {\includegraphics[width=5cm]{png/WP716_74442.png}};
\node at (4,2) [inner sep = 0pt] (pathway4) {\includegraphics[width=5cm]{png/WP706_74443.png}};
\node [above left = of pathway2] (pathway5) {\includegraphics[width=4cm]{png/WP1591_73381.png}};
\end{tikzpicture}
};


This results in the following cloud:

There is to much white space to my liking. I prefer the line of the cloud the just barely touch the figures included. According to an answer here, I should use inner sep=0cm. However the white space surrounding the figures remain.

What I need is a cloud that is drawn around a set of figures in png format. What do I need to do, to get a smaller cloud (with less white space).

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Did you try a negative inner sep value? –  Paul Gessler Jul 24 '14 at 12:18
@PaulGessler Great that did it. Didn't know you could provide negative values. –  Nonsense Jul 24 '14 at 12:24

The key inner sep may have negative values. So you can use this to adjust to your liking the size of the shape relative to the images. But, as noted by percusse in a comment, negative inner sep values can lead to nasty overlap and miscalculated bounding boxes that may show up if you have other things in the drawing. Note also that nesting tikzpictures is generally liable to cause problems (c.f. 1 2 3 4 5), but in this case it works fine.

A better approach would be to use the fit library, as I've shown here, which avoids the nested tikzpictures. This also has the benefit of requiring less drastic adjustments to inner sep. For example, in this code I was able to use inner sep=0pt and I think it fits close enough. As they say in many cookbooks, "season to taste."

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}
% draw the named nodes
\node (a) at (0,0) [inner sep = 0pt] {\includegraphics[width=5cm]{example-image-a}};
\node (b) at (4,1) [inner sep = 0pt] {\includegraphics[width=5cm]{example-image-b}};
% draw the cloud node, fitted to named nodes (a) and (b)
\node [draw, inner sep=0pt, cloud, cloud puffs=20, aspect=2,fit=(a) (b)] {};
\end{tikzpicture}
\end{document}


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May take negative values but shouldn't. Try \tikz{\node[draw] (a) at (0,0) [inner sep = -5pt] {\Huge A}; \draw (a) -- (5mm,0);}. It leads to miscalculated bounding boxes too. –  percusse Jul 24 '14 at 13:27
Thanks @percusse; updated with a note to this effect. –  Paul Gessler Jul 24 '14 at 15:12