Create a custom figure/image source list

Question

I've reviewed the answers at Add source to figure caption question and tried to adapt them for what I am trying to achieve. Unfortunately I can't get the result I'm looking for. What I am trying to do is create a source command where I can enter the source of the figure but that it does not show up under the figure caption as in the linked question but remains invisible at this point. I would like to create a listof environment that I can use in an appendix that would be able to refer back to the figure number and contain the source description. My reason for this is that I'm writing a Humanities thesis and the source description of some of the images from Archives can be quite long.

Below is a MWE (I'm using memoir class) of what I have tried so far but the problem I have is that the caption shows under the figure and nothing shows in my listof environment.

\documentclass[oneside]{memoir}
\renewcommand{\insertchapterspace}{}

\newcommand*{\source}{}
\newcommand{\listsourcename}{Picture sources}
\newlistof{listofsources}{los}{\listsourcename}
\newlistentry{source}{los}{0}

\begin{document}
\tableofcontents*
\listoffigures
\mainmatter
\chapter{foo}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[A figure]{A longer image description}
\source{Source of the image.}
\end{figure}

\chapter{bar}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[Another figure]{Another longer image description}
\source{Source of another image.}
\end{figure}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[Again Another figure]{Again Another longer image description}
\source{Source of another image again.}
\end{figure}

\appendix
\listofsources

\end{document}

What I would like is not to have the source caption under the figure but a listing that would give out the following if the MWE is used.

Picture Sources

1.1: Source of the image

2.1: Source of another image

2.2: Source of another image again.

Answer 1

Something like this? Use \source{Some text} to add something to the los file.

\documentclass[oneside]{memoir}
\renewcommand{\insertchapterspace}{}

\newcommand{\listsourcename}{Picture sources}
\newlistof{listofsources}{los}{\listsourcename}

\newcommand*{\source}[1]{\addcontentsline{los}{section}{\protect\numberline{\thefigure}#1}}


\begin{document}

\tableofcontents*

\listoffigures

\mainmatter
\chapter{foo}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[A figure]{A longer image description}
\source{Source of the image.}
\end{figure}

\chapter{bar}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[Another figure]{Another longer image description}
\source{Source of another image.}
\end{figure}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[Again Another figure]{Again Another longer image description}
\source{Source of another image again.}
\end{figure}

\appendix
\listofsources

\end{document}

New version, with memoir's version of tocloft emulation (a little bit strange, in my point of view), removing the page number and the dots in the numberline.

\documentclass[oneside]{memoir}
\renewcommand{\insertchapterspace}{}

\newcommand{\listsourcename}{Picture sources}
\newlistof{listoffiguresource}{los}{\listsourcename}
\newlistentry{figuresource}{los}{0}% 
\setcounter{losdepth}{1}

\renewcommand{\cftfiguresourcedotsep}{1000}
\newcommand*{\source}[1]{\addtocontents{los}{\protect\contentsline{figuresource}{\thefigure:~#1}{}}}

\begin{document}

\tableofcontents*

\listoffigures

\mainmatter
\chapter{foo}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[A figure]{A longer image description}
\source{Source of the image.}
\end{figure}

\chapter{bar}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[Another figure]{Another longer image description}
\source{Source of another image.}
\end{figure}

\begin{figure}
\centering
\rule{1cm}{1cm}
\caption[Again Another figure]{Again Another longer image description}
\source{Source of another image again.}
\end{figure}

\appendix
\listoffiguresource

\end{document}