This is not a complete solution, but I hope it might be useful.
The main idea is to compose a list of "unreliable" sources
\gdef\unreliable{}
\listadd{\unreliable}{LinkD01}
\listadd{\unreliable}{LinkC04}
and then to use the following citation command, which has the usual format \mycite[prenote][postnote]{key}:
\usepackage{xparse}
\DeclareDocumentCommand{\mycite}{oom}{%
\ifinlist{#3}{\unreliable} %in the list of 'reliables'?
{\IfNoValueTF{#2}
{\IfNoValueTF{#1}
{\footfullcite{#3}}
{\footfullcite[#1]{#3}}}
{\footfullcite[#1][#2]{#3}}}
{\IfNoValueTF{#2}
{\IfNoValueTF{#1}
{\cite{#3}}
{\cite[#1]{#3}}}
{\cite[#1][#2]{#3}}}}
As you see, \mycite doesn't fully support the citing of several keys.
If you add keys to the \unreliable list manually using \listadd, this is basically enough to solve the problem. But it's also possible to populate the list automatically. To do this we first define a special bibenvironment
\defbibenvironment{counting}
{}
{}
{\listxadd{\unreliable}{\thefield{entrykey}}}
and then fill in the list in the beginning of the document:
\begingroup%
\makeatletter%
\def\blx@driver#1{}%
\printbibliography[env=counting,heading=none,keyword=secondary]%
\makeatother%
\endgroup%
The list will contain all sources with the keyword secondary.
For I don't know what reason the \ifinlist command didn't work for me in this automatic case. So in the MWE below I use instead the following command:
\newtoggle{tempa}
\newcommand{\ifunreliable}[3]{%
\renewcommand*{\do}[1]{%
\togglefalse{tempa}%
\ifstrequal{#1}{##1}
{\toggletrue{tempa}\listbreak}
{}}%
\dolistloop{\unreliable}%
\iftoggle{tempa}{#2}{#3}%
}
Full MWE with automatic list filling:
\documentclass{article}
\usepackage{filecontents}
\begin{filecontents}{biblatextest1.bib}
@BOOK{BookA03,
author = {Author Aaa},
title = {Some Title},
publisher = {Some Publisher},
year = 2003,
}
@BOOK{BookB02,
author = {Author Bbb},
title = {Some Title},
publisher = {Some Publisher},
year = 2002,
}
\end{filecontents}
\begin{filecontents}{biblatextest2.bib}
@MISC{LinkC04,
author = {Author Ccc},
title = {Some Title},
year = 2004,
url = {www.test1.com/bild.jpg},
}
@MISC{LinkD01,
author = {Author Ddd},
title = {Some Title},
year = 2001,
url = {www.test2.com/bild.jpg},
}
\end{filecontents}
\usepackage[style = alphabetic, labelnumber, defernumbers = true, backend = biber]{biblatex}
\addbibresource{biblatextest1.bib}
\addbibresource{biblatextest2.bib}
\usepackage{hyperref}
%Append keywords to identify different bibliography entries.
\DeclareSourcemap{
\maps[datatype=bibtex, overwrite]{
\map{
\perdatasource{biblatextest1.bib}
\step[fieldset=KEYWORDS, fieldvalue=primary, append]
}
\map{
\perdatasource{biblatextest2.bib}
\step[fieldset=KEYWORDS, fieldvalue=secondary, append]
}
}
}
\DeclareFieldFormat{labelnumberwidth}{\mkbibbrackets{#1}}
\defbibenvironment{bibliographyNUM}
{\list
{\printtext[labelnumberwidth]{%
\printfield{prefixnumber}%
\printfield{labelnumber}}}
{\setlength{\labelwidth}{\labelnumberwidth}%
\setlength{\leftmargin}{\labelwidth}%
\setlength{\labelsep}{\biblabelsep}%
\addtolength{\leftmargin}{\labelsep}%
\setlength{\itemsep}{\bibitemsep}%
\setlength{\parsep}{\bibparsep}}%
\renewcommand*{\makelabel}[1]{\hss##1}}
{\endlist}
{\item}
\assignrefcontextkeyws[sorting=none]{secondary}
\gdef\unreliable{}
\defbibenvironment{counting}
{}
{}
{\listxadd{\unreliable}{\thefield{entrykey}}}
\newtoggle{tempa}
\newcommand{\ifunreliable}[3]{%
\renewcommand*{\do}[1]{%
\togglefalse{tempa}%
\ifstrequal{#1}{##1}
{\toggletrue{tempa}\listbreak}
{}}%
\dolistloop{\unreliable}%
\iftoggle{tempa}{#2}{#3}%
}
\usepackage{xparse}
\DeclareDocumentCommand{\mycite}{oom}{%
\ifunreliable{#3}
{\IfNoValueTF{#2}
{\IfNoValueTF{#1}
{\footfullcite{#3}}
{\footfullcite[#1]{#3}}}
{\footfullcite[#1][#2]{#3}}}
{\IfNoValueTF{#2}
{\IfNoValueTF{#1}
{\cite{#3}}
{\cite[#1]{#3}}}
{\cite[#1][#2]{#3}}}}
\begin{document}
\begingroup%
\makeatletter%
\def\blx@driver#1{}%
\printbibliography[env=counting,heading=none,keyword=secondary]%
\makeatother%
\endgroup%
The first two citations \mycite{LinkD01} and \mycite{BookB02}.
The others are \mycite{LinkC04} and \mycite{BookA03}.
\printbibliography[title=Bibliography, keyword=primary]
\newrefcontext[sorting=none]
\printbibliography[env=bibliographyNUM,title=References, keyword=secondary, resetnumbers]
\end{document}
\cite{foo,bar}wherefooshould get an alphabetic style andbarshould go to the footnote.) Then things become a bit more intricate - even more than changing between numeric and alphabetic. – moewe Sep 14 '16 at 12:41