How to cite references as numbered (numeric) "footnotes" in Beamer with BibLaTeX?

Question

I'm working on a scientific beamer presentation. One demand is to put numbered references relevant to each slide into its footnotes. Apart from space concerns, this also leads to a number of questions:

• \footcite obviously creates a footmark wherever it's used. But since my references are supposed to be relevant for the entire slide, as opposed to, say, one bullet point, I want to suppress the footmark from appearing. In this question, the usage of \footnotetext has been proposed, but can this help for BibLaTeX' \footcite command, or do we need some kind of workaround?
• Ideally, I want the footnote to be of the form "[X] full reference", so again we need to suppress the footnote mark at the front. The "X" would be the number corresponding to the citation order. One idea to realize this could be to cite once using numeric style, and a second time with verbose style. But then how to get rid of the footnote mark?

As wished, here's a minimal example:

\documentclass{beamer}
\beamertemplatenavigationsymbolsempty
\setbeamerfont{footnote}{size=\tiny}

\usepackage{filecontents}

\begin{filecontents}{test-bib.bib}
    @online{firstSource,
        title = "This is my first source",
        author = "Robert Petersson",
        url = "https://www.my-new-website.org/firstSub/secondSub/thirdSub.htm", % As to simulate realistically long URLs
    }

    @article{secondSource,
        author = "Peter Parker",
        title = "Another Source",
        journaltitle = "Unknown Journal",
        date = "2012-12-21",
        url = "https://www.example.org",
        urldate = "2012-12-30"
    }

    @image{anImageSource,
        author = "Image Creator",
        title = "Paper in which image was found",
        date = "2013-04-05"}
\end{filecontents}

\usepackage[
    sorting=none, % Use citation order
    style=numeric % Primarily cite numbers
%   style=verbose % Primarily cite full reference
]{biblatex}
\addbibresource{test-bib.bib}

\begin{document}
     \begin{frame}{My test frame}
        \footnotetext[1]{\cite{firstSource} \fullcite{firstSource}}
        \footnotetext[2]{\cite{secondSource} \fullcite{secondSource}}
        \footnotetext[3]{\cite{anImageSource} \fullcite{anImageSource}}

        \begin{figure}
            \includegraphics[width=.3\linewidth]{example-image-a}
            \caption{Example Image A\footnotemark[3]}
        \end{figure}

    \end{frame}
\end{document}

So, in short: How do I realize footnotes of the form "[X] full reference", completely suppressing all of the little numbers footnotes usually produce? The \fullcite which Marijn suggested already comes quite close to it. Now just how to get rid of the footnote marks?

Answer 1

I've now come up with the following workaround:

\documentclass{beamer}
\beamertemplatenavigationsymbolsempty
\setbeamerfont{footnote}{size=\tiny}

\usepackage{filecontents}

\begin{filecontents}{test-bib.bib}
    @online{firstSource,
        title = "This is my first source",
        author = "Robert Petersson",
        url = "https://www.my-new-website.org/firstSub/secondSub/thirdSub.htm", % As to simulate realistically long URLs
    }

    @article{secondSource,
        author = "Peter Parker",
        title = "Another Source",
        journaltitle = "Unknown Journal",
        date = "2012-12-21",
        url = "https://www.example.org",
        urldate = "2012-12-30"
    }

    @image{anImageSource,
        author = "Image Creator",
        title = "Paper in which image was found",
        date = "2013-04-05"}
\end{filecontents}

\usepackage[
sorting=none, % Use citation order
style=numeric % Primarily cite numbers
%   style=verbose % Primarily cite full reference
]{biblatex}
\addbibresource{test-bib.bib}

\usepackage{tabularx}
\newcommand*{\doublecite}[1]{\cite{#1}&\fullcite{#1}\\}

\newcommand*{\fakefootnotes}[1]{%
    \vfill
    \rule{.5\linewidth}{.5pt}\\[.5em]
    {\tiny
        \begin{tabularx}{\linewidth}{@{}l@{\hspace{1mm}}X}
            #1
        \end{tabularx}
    }
}

\begin{document}
    \begin{frame}{My test frame}

        \begin{figure}
            \includegraphics[width=.3\linewidth]{example-image-a}
            \caption{Example Image A \cite{anImageSource}}
        \end{figure}

        \fakefootnotes{
            \doublecite{anImageSource}
            \doublecite{firstSource}
            \doublecite{secondSource}
        }
    \end{frame}
\end{document}

Instead of actually using LaTeX' footnote mechanism, I only mock them up. In fact, I even think that this tabular solution looks reasonably good. There's only one problems with it:

While the footnotes may be floating to the bottom of the text area as intended, there's still much space below it (as opposed to the MWE given in the question, where the footnotes use up all the bottom space). I assume the reserved space is the footer. In my specific case this won't be a problem, since the footer in my presentation is used. One concern might be though that the \vfill forces all above text to be top-aligned.