figure environment doesn't work in poster latex

I am creating a poster and for some reason, this doesn’t work:

begin{figure}
   centering
   includegraphics[scale=0.6]{Fig/pic.pdf}
   caption{BLAHBALH}
end{figure}

It doesn’t produce any error, it only doesn’t show anything in the poster. However this works:

begin{center}
   includegraphics[scale=0.6]{Fig/pic.pdf}
end{center}

Why?

begin{tikzfigure}[Insert Caption Here]
      includegraphics[width=0.9linewidth]{filename.png}
end{tikzfigure}