Lyx+article document, image under title in front page

One could of course create a custom titlepage from scratch, rather than using the Title, Author, etc. layouts from the dropdown menu. A quick alternative workaround/hack is to place the image as part of the title. If you don't need any vertical space between title and image, hit Ctrl + Enter just after the title, and insert the image with Insert --> Graphics, as usual.

If you need some vertical space, rather than Ctrl + Enter insert an ERT with Ctrl + L, write \\[1cm] (modify the length to suit your need), and insert the image right after this, as in this screenshot:

Well my suggestion was a little bit more LaTeX option. Useful in LyX I think, but perhaps not so easy as the solution suggested by @TorbjørnT.

Well you can use the environment \titlepage for create your own frontpage. By example:

%% LyX 2.0.6 created this file.  For more info, see http://www.lyx.org/.
%% Do not edit unless you really know what you are doing.
\documentclass[italian]{scrreprt}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{geometry}
\geometry{verbose,lmargin=2cm,rmargin=2cm}
\setcounter{secnumdepth}{3}
\setcounter{tocdepth}{1}
\usepackage{float}
\usepackage{textcomp}
\usepackage{graphicx}
\PassOptionsToPackage{normalem}{ulem}
\usepackage{ulem}

\makeatletter
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Textclass specific LaTeX commands.
\newenvironment{lyxcode}
{\par\begin{list}{}{
\setlength{\rightmargin}{\leftmargin}
\setlength{\listparindent}{0pt}% needed for AMS classes
\raggedright
\setlength{\itemsep}{0pt}
\setlength{\parsep}{0pt}
\normalfont\ttfamily}%
\item[]}
{\end{list}}

\makeatother

\usepackage{babel}

\begin{document}

\begin{titlepage}
\setlength{\parindent}{0pt}
\setlength{\parskip}{0pt}
\vspace*{\stretch{1}}
%\rule{\linewidth}{1pt}
\begin{flushright}
{\Huge Linee guida utilizzo} %\\ [14pt]
\end{flushright}
\begin{center}
\includegraphics[width=\textwidth]{your_image.jpg}
\end{center}
\begin{flushright}
\huge Caterpillar
\end{flushright}
\vspace*{\stretch{2}}
\begin{center}
\textsc{7 decembre 2013}
\end{center}
\end{titlepage}

\end{document}

You can check an example here. I hope this will be helpful.

Regards