If you're already using the float
package, then it's easy to set up a new kind of float for your Plate images:
\documentclass{article}
\usepackage{float}
\usepackage[demo]{graphicx}
\usepackage{kantlipsum}% for dummy text
\newfloat{plate}{pb}{plt} % second argument should be {htbp} in your actual document
\floatname{plate}{Plate}
\begin{document}
\listoffigures
\listof{plate}{List of Plates}
\section{A section}
\kant[1-2]
\begin{figure}[bp]
\centering
\includegraphics[width=2in]{fig}
\caption{A figure}
\end{figure}
\kant[2]
\begin{plate}
\centering
\includegraphics[width=3in]{plate}
\caption{A plate}
\end{plate}
\kant[3]
\end{document}

If you also want to use the caption
package to manage caption formatting, you can achieve the same result with the newfloat
package, which is more compatible with caption
. The code is almost the same:
\documentclass{article}
\usepackage{newfloat}
\usepackage[demo]{graphicx}
\usepackage{kantlipsum}% for dummy text
\DeclareFloatingEnvironment{plate}
\begin{document}
\listoffigures
\listofplates
\section{A section}
\kant[1-2]
\begin{figure}[bp]
\centering
\includegraphics[width=2in]{fig}
\caption{A figure}
\end{figure}
\kant[2]
\begin{plate}
\centering
\includegraphics[width=3in]{plate}
\caption{A plate}
\end{plate}
\kant[3]
\end{document}