configure latex figure without borders

Question

My latex code below put a border around subfigures.

\documentclass{bmcart}

%%% Load packages
\usepackage{graphicx}
\usepackage[utf8]{inputenc} %unicode support
% Para inserir figuras lado a lado.
\usepackage{subfigure}

%%% Begin ...
\begin{document}
\subsection*{Figure 3}
    \begin{figure}
        \subfigure[MLP]{\label{fig:a}\includegraphics[width=60mm, trim=4 4 4 4,clip]{img/mlp.png}}
        \subfigure[ANFIS]{\label{fig:b}\includegraphics[width=60mm, trim=4 4 4 4,clip]{img/anfis.png}}
        \subfigure[SVM]{\label{fig:c}\includegraphics[width=60mm, trim=4 4 4 4,clip]{img/svm.png}}
        \subfigure[DT]{\label{fig:d}\includegraphics[width=60mm, trim=4 4 4 4,clip]{img/dt.png}}
        \caption{Exemplos dos quatro diferentes modelos de algoritmos utilizando aprendizado de máquina~\cite{Hassan2017}}
    \end{figure}
\end{document}

This code, generate this image:

I need to remove this border!! Any help is welcome!!