Each "blob" can be drawn using a technique taken from this answer, but modified to use Hobby package which produces smoother results.
In the next example I define a pic which draws one of these "blobs". Being a pic is very easy to rotate, scale and translate the shape, so I draw 35 of them in a regular grid. Instead of a regular grid you can use the random positions generated by a Poisson disc sampling.
This is my minimal example code:
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{hobby}
\usetikzlibrary{calc}
\begin{document}
\tikzset{
pics/blob/.style={
code={
\draw[use Hobby shortcut, fill, closed] (0,0) +($(0:1+4*rnd)$)
\foreach \a in {60,120,...,350} { .. +($(\a: 1+4*rnd)$) };
}
}}
\begin{tikzpicture}
\foreach \x in {0,...,5} {
\foreach \y in {0,...,7} {
\pgfmathsetmacro{\scale}{0.1+0.1*rnd}
\pic at (\x,\y) [fill=green!30, scale=\scale, rotate=360*rnd]{blob};
}
};
\end{tikzpicture}
\end{document}
And this is the result:
Update: using Poisson sampling
Using the lua code from this answer the (x,y) of each blob is generated. The remaining of the code is the same. This is the complete main tex file:
\documentclass{article}
\usepackage{tikz}
\usepackage{poisson}
\usetikzlibrary{hobby}
\usetikzlibrary{calc}
\tikzset{
pics/blob/.style={
code={
\draw[use Hobby shortcut, fill, closed] (0,0) +($(0:1+4*rnd)$)
\foreach \a in {60,120,...,350} { .. +($(\a: 1+4*rnd)$) };
}
}}
\begin{document}
\edef\mylist{\poissonpointslist{5}{5}{0.4}{15}}
\begin{tikzpicture}
\foreach \x/\y in \mylist {
\pgfmathsetmacro{\scale}{0.02+0.1*rnd}
\pic at (\x,\y) [fill=green!30, scale=0.1, rotate=360*rnd]{blob};
}
\end{tikzpicture}
\end{document}
And this is the result:
To compile it you have to use Lualatex (it takes a while to complete).
Final update
This version uses the code in the OP's question, and then my code to fill its nodes. It was necessary to tweak the scale of the blobs, because the area to fill is very small, and the line width of the blobs for the same reason. Also, inner sep=0pt was added to the OP's nodes, to have full control over their width and height.
Finally, since in the figure provided by the OP both boxes are filled exactly with the same shapes, but in a different color, I fixed a random seed and restored it before filling the second box.
The code:
\documentclass{article}
\usepackage{tikz}
\usepackage{poisson}
\usetikzlibrary{hobby}
\usetikzlibrary{calc}
\usetikzlibrary{positioning}
\tikzset{
pics/blob/.style={
code={
\draw[use Hobby shortcut, fill, closed] (0,0) +($(0:1+4*rnd)$)
\foreach \a in {60,120,...,350} { .. +($(\a: 1+4*rnd)$) };
}
}}
\newcounter{mathseed}
\setcounter{mathseed}{3}
\begin{document}
\edef\mylist{\poissonpointslist{1}{.9}{0.06}{10}}
\begin{tikzpicture}[every node/.style={draw,thin,minimum height=10mm,inner sep=0pt}]
\node [fill=orange,text width=2mm] (boxA) {};
\node [text width=11mm,anchor=west] at (boxA.east) (boxB) {};
\node [anchor=west, text width=2mm] at (boxB.east) (boxC) {};
\node [text width=11mm,anchor=west] at (boxC.east) (boxD) {};
\node [fill=black!30,anchor=west, text width=2mm] at (boxD.east) (boxE) {};
\pgfmathsetseed{\arabic{mathseed}}
\foreach \x/\y in \mylist {
\pgfmathsetmacro{\scale}{0.01+0.01*rnd}
\pic at ($(boxB.south west)+(\x+.06,\y+.05)$)
[line width=0.05mm,fill=green!80!black,
scale=\scale, rotate=360*rnd]{blob};
}
\pgfmathsetseed{\arabic{mathseed}}
\foreach \x/\y in \mylist {
\pgfmathsetmacro{\scale}{0.01+0.01*rnd}
\pic at ($(boxD.south west)+(\x+.06,\y+.05)$)
[line width=0.05mm,fill=magenta!80!black,
scale=\scale, rotate=360*rnd]{blob};
}
\end{tikzpicture}
\end{document}
The result:
