We can use the graphicx package together with the graphicspath command to specify the looking up path for pictures. A typical structure may look like this:

\usepackage{graphicx}
% Must use this command BEFORE you begin document!
\graphicspath{{pic_path1/}{pic_path2}}
\begin{document}
% some content
\end{document}


As you can see, the syntax of graphicspath command is very simple. You just enclose your picture path, either relative to current work path, or absolute path, in a pair of curly braces. Note that you must place this command before you begin document otherwise it will take no effect.

Please refer to this page for more details about graphicspath command.