documentclass[11pt]{standalone}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage{tikz}
usepackage{pgfplots}

% draw a circle of radius #1 with randomness #2
newcommandirregularcircle[2]{%
  pgfextra {%
    pgfmathsetseed{42}%
    pgfmathsetmacrolen{(#1)+rand*(#2)}}
  +(0:len pt)
  foreach a in {20,40,...,340}{
    pgfextra {pgfmathsetmacrolen{(#1)+rand*(#2)}}
    -- +(a:len pt)
  } -- cycle
}

begin{document}
begin{tikzpicture}[auto]
  begin{axis}[%
    axis x line=center,
    axis y line=center,
    xmin=-8, xmax=8,
    ymin=-8, ymax=8,
    ]
    draw[rounded corners=2mm, fill=black, opacity=0.2] (axis cs:0,0) irregularcircle{2cm}{2mm};
  end{axis}
end{tikzpicture}
end{document}