n=150;
h=Table[
f=ToString[NumberForm[i,7,NumberPadding->{"0",""}]]<>".jpg";
a=Import[f];
r=PixelValue[a,{270,121;;380}]//Transpose//First;
r1=ListConvolve[{1,5,15,30,45,51,45,30,15,5,1 },r]//Round;
m=Nearest[r1,Max[r1]/2,1]//First;
p=Position[r1,m][[1,1]],{i,n}];

f=Fit[h,{1,x,x^2},x];
Show[ListPlot[h,PlotStyle->Red],Plot[f,{x,1,n}]]