SetDirectory["C:\\drorbn\\AcademicPensieve\\Classes\\15-344-Combinatorics"]

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]
]
];

?Make

target= "DayOne.png";
sources = {"FrontPage-150915.png", "About-150915-1.png", "About-150915-2.png"};
Make[target, sources⋃{"one/Day_One_Handout.pdf"}, Hold[
Read["!convert -density 200 -background white -alpha remove one/Day_One_Handout.pdf Day_One_Handout.png"];
Read["!montage -geometry 1700x2200+0+0 -background white -tile 2x2 "<>StringJoin[(#<>" ")& /@ sources]<>"Day_One_Handout.png "<>target];
]]

target= "Hour3.png";
source = "one/Hour_3_Handout.pdf";
Make[target, source, Hold[
Read["!convert -density 200 -background white -alpha remove "<>source<>" "<>target];
]]

{
"TitleNotes" -> "This is my personal notebook for my 2015 <a href=http://drorbn.net/?title=15-344>MAT 344 Combinatorics</a> class. <span style=\"color: red;\">Use at your own risk.</span><p>",
"CleanTeX" -> True
}