tabular vertical alignment to top?

\def\imagetop#1{\vtop{\null\hbox{#1}}}

\begin{tabular}{c|c}
  \emph{Normal} & \emph{Cone} \\
  \imagetop{\includegraphics[width=0.39\textwidth]{images/pipe1}}&
  \imagetop{\includegraphics[width=0.61\textwidth]{images/pipe1}}
\end{tabular}

The topic has been discussed (and solved) in German here: http://www.matheplanet.com/matheplanet/nuke/html/viewtopic.php?topic=133671

In your case, try:

\begin{tabular}[h]{ c | c}
    \emph{Normal} & \emph{Cone} \\
    \raisebox{-\height+\baselineskip}{\includegraphics[width=0.39\textwidth]{images/pipe1}} &
    \raisebox{-\height+\baselineskip}{\includegraphics[width=0.61\textwidth]{images/pipe2}}
\end{tabular}

This should also solve the problem of the empty line above.

If you would like to stick with the imagetop command, try:

\def\imagetop#1{\raisebox{-\height+\baselineskip}{#1}}

Regarding WLanger's question about Alexey's solution: to adjust for the empty line on top of the image, put the text into a \parbox, and use \raisebox (with a negative value) to adjust it's vertical position.

\raisebox{value}{your text here} % will lower text if it has a negative value.

\parbox{width}{your text here} % will allow for text wrapping

You will have to nest them, like this:

\raisebox{value}{\parbox{width}{your text goes here}}

So the result will be this:

\def\imagetop#1{\vtop{\null\hbox{#1}}}

\begin{tabular}[h]{c|c}        
  \emph{Normal} & \emph{Cone} \\        
  \imagetop{\includegraphics[width=0.39\textwidth]{images/pipe1}} & \raisebox{-1cm}{\parbox{8cm}{Replace this with your text, and adjust the raisebox and parbox values to your liking. I don't know the measurements of the images you're using or I'd do it for you.}
  \imagetop{\includegraphics[width=0.61\textwidth]{images/pipe1}}
\end{tabular}

It isn't elegant, but it works!