I have a problem with the headers. I want to keep the image header but remove the text header (small word contents).

Below is the code:

\documentclass[11pt,a4paper,titlepage]{article}

\usepackage{lipsum}
\usepackage{graphicx}
\usepackage[a4paper,margin=1.0in]{geometry}
\usepackage{fancyhdr}
\pagestyle{fancy}
\renewcommand{\footrulewidth}{0pt}
\cfoot{\includegraphics[width=\textwidth]{Footer}}

\begin{document}
\title{\vspace{-30mm}\Huge Compressed Air}
\date{\Large ATLAS COPCO}
\maketitle
\tableofcontents
\thispagestyle{fancy}
\end{document}


\fancyhf{} % Clear header/footer

otherwise document elements that address header/footer location you have not updated may still influence it. In your case, you haven't cleared what is contained in \lhead, \rhead, \lfoot and \rfoot. The above macro is shorthand for and clears all six locations (including \chead and \cfoot).
So, add the above in your preamble just after loading fancyhdr or at the start of setting your fancy page style.