SetDirectory["C:\\drorbn\\AcademicPensieve\\Talks\\CUMC-200820"]

Make::usage = "Make[targets, sources, action] makes a target, or a list of targets, given sources, or a list of sources, in the style of the unix 'make' command.";
Make[target_String, sources_, action_Hold] := Make[Evaluate@{target}, sources, action];
Make[targets_, source_String, action__Hold] := Make[targets, Evaluate@{source}, action];
Make[targets_List, sources_List, action_Hold] := Module[{},
If[
(And @@ ((FileType[#] =!= None)& /@ sources)) &&
Or[
Or @@ ((FileType[#]===None)& /@ targets),
Min[AbsoluteTime[FileDate[#]]& /@ targets] < Max[AbsoluteTime[FileDate[#]]& /@ sources]
],
Print["Making ",targets, " ..."];
ReleaseHold[action]
]
];

targets ={"Proof.png", "Dance.png"};
source = "Quintic-Handout.pdf";
dpi=150;
pos=Get["Quintic-Handout.pos"];
pos1=dpi(11.69-pos[[1]]) // Round; yoff1=pos1[[1]]// ToString; ylen1=pos1[[2]]-pos1[[1]] // ToString;
pos2=dpi(11.69-pos[[2]]) // Round; yoff2=pos2[[1]]// ToString; ylen2=pos2[[2]]-pos2[[1]] // ToString;
Make[targets, source, Hold[
Read["!convert -density 150 -background white -alpha remove -crop x"<>ylen1<>"+0+"<>yoff1<>" -trim "<>source<>"[0] Proof.png"];
Read["!convert -density 150 -background white -alpha remove -crop x"<>ylen2<>"+0+"<>yoff2<>" -trim "<>source<>"[1] Dance.png"];
MakeThumb /@ targets;
]]

{
"TitleNotes" -> "This is the construction folder for my talks in Sydney, August 2017, <a href=http://www.math.toronto.edu/~drorbn/Talks/Sydney-1708/>http://www.math.toronto.edu/~drorbn/Talks/Sydney-1708/</a>.<p>",
"CleanTeX" -> True
}