Simple solution to add a shaded image border

Question

I want to make a shaded image border. My current solution is using \shadowbox:

 \documentclass[12pt]{article}
 \usepackage{tikz}
 \usepackage{fancybox, graphicx}  

 \begin{document}
    \shadowsize=1mm
    \color{blue}
    \shadowbox{\fboxsep=3mm\fcolorbox{white}{white}{\includegraphics[width=12cm,height=8cm,keepaspectratio]{example-image-a}}}
\end{document}

So 1) there must be a white border 2) which casts a shadow. But this creates a very "simple", solid shadow:

I would like to achieve a more "blurry effect".

Based on this answer I wrote something like this:

\documentclass[12pt]{article}
\usepackage{tikz}
\usepackage[skins]{tcolorbox}
\usepackage{fancybox, graphicx}

\begin{document}
  \begin{center}
      \begin{tcolorbox}[enhanced,width=12cm,height=8cm, center upper,
          fontupper=\large\bfseries,drop fuzzy shadow southeast,
          boxrule=0.4pt,sharp corners,colframe=yellow!80!white,colback=white!10]

      \includegraphics[width=12cm,height=7.9cm,keepaspectratio]{example-image-a}
      \end{tcolorbox}
      \end{center}
\end{document}

but as you can see, I need this colorbox to scale with my image (which is max 8x12cm, keeping aspect ratio).

I saw some overly complicated answers with applying some rules but I really believe there must be a simpler solution.

Besides - can the above solution actually drop shadows to 4 sides of the world, not only southeast etc?

Answer 1

\tcolorbox is either using the \linewidth or the sizes specified with width and height which may be wrong considering the internal content.

\tcbox changes the size according to the inner content and scales appropriately.

I have defined a \whiteshadowbox with some options, the centering is done with the before and after keys.

\documentclass[12pt]{article}
\usepackage[skins]{tcolorbox}

\newtcbox{\whiteshadowbox}[1][]{%
  enhanced, 
  center upper,
  fontupper=\large\bfseries,
  drop fuzzy shadow southeast,
  boxrule=0.4pt,
  sharp corners,
  colframe=blue,
  colback=white!10,
  before={\begin{center}},
    after={\end{center}},
  #1%
}

\begin{document}
  \whiteshadowbox{%
    \includegraphics[width=12cm,height=7.9cm,keepaspectratio]{example-image-a}
  }

  \whiteshadowbox[colback=green]{%
    \includegraphics[width=5cm,height=6cm,keepaspectratio]{example-image-a}
  }
\end{document}

Update with halo option

\documentclass[12pt]{article}
\usepackage[skins]{tcolorbox}

\newtcbox{\whiteshadowbox}[1][]{%
  enhanced, 
  center upper,
  fontupper=\large\bfseries,
  fuzzy halo={0.9mm with gray},
%  drop fuzzy shadow southeast,
  boxrule=0.4pt,
  sharp corners,
  colframe=blue,
  colback=white!10,
  before={\begin{center}},
    after={\end{center}},
  #1%
}

\begin{document}
  \whiteshadowbox{%
    \includegraphics[width=12cm,height=7.9cm,keepaspectratio]{example-image-a}
  }

  \whiteshadowbox[colback=green]{%
    \includegraphics[width=5cm,height=6cm,keepaspectratio]{example-image-a}
  }
\end{document}

With size=tight and boxsep=1cm settings

\documentclass[12pt]{article}
\usepackage[skins]{tcolorbox}

\tcbset{
  halobox/.style={
    enhanced,
    center upper,
    fontupper=\large\bfseries,
    size=tight,
    boxsep=1cm,
    fuzzy halo={0.9mm with gray},
    boxrule=0.4pt,
    sharp corners,
    colframe=blue,
    colback=white!10,
    before={\begin{center}},
      after={\end{center}}}
  }

\newtcbox{\whiteshadowbox}[1][]{%
  halobox,
  #1%
}

\begin{document}
  \whiteshadowbox{%
    \includegraphics[width=12cm,height=7.9cm,keepaspectratio]{example-image-a}
  }

  \whiteshadowbox[colback=green]{%
    \includegraphics[width=5cm,height=6cm,keepaspectratio]{example-image-a}
  }
\end{document}

Answer 2

It's is very simple with the pstricks module pst-blur:

\documentclass[12pt, svgnames]{article}
\usepackage{graphicx}
\usepackage{pst-blur} 
%\usepackage{auto-pst-pdf}% to compile with pdflatex --enable-write18 (MiKTeX) or pdflatex --shell-escape (TeXLive, MacTeX)

 \begin{document} 

\begin{pspicture}
 \psframebox[linecolor = RoyalBlue, framesep = 4mm, shadow, blur, shadowcolor = RoyalBlue, shadowsize = 1.5mm ]{%
 \includegraphics[width = 12cm, height = 8cm, keepaspectratio]{example-image-a}}
\end{pspicture}

\end{document}