how to add notes that start on the left side?

Question

I would like to add notes under the caption of my images. The notes shouldn't be centred but start of the left side. And is there a way to control the vertical distance of the notes from the caption like caption from the image \captionsetup[figure]{font=normalsize,skip=20pt}?

\documentclass[12pt,a4paper]{article}
\usepackage[top=1in, bottom=1in, inner=1in, outer=1in]{geometry}
\usepackage[onehalfspacing]{setspace}
\usepackage[utf8]{inputenc}
\usepackage{ngerman}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{caption}
\captionsetup[figure]{font=normalsize,skip=20pt}

\begin{document}

        \begin{figure}[!htb]
            \centering
            \includegraphics[width=\textwidth,height=\textheight,keepaspectratio]{untitled.png}
            \caption{Lohn und Alter}
            %add source/comment whole width
        \end{figure}

        \begin{figure}[!htb]
            \centering
            \includegraphics[scale=0.25]{untitled.png}
            \caption{Lohn und Alter}
            %add source/comment, whole width
        \end{figure}

\end{document}