I found a solution for my problem. Thank you for providing the proper code for ordering, but in this case out of some reason resizing the picture (a miniscule amount even) took care of the "Dimensions too large" error. I guess some meta-data in the picture messed the whole thing up (maybe because it's a SEM-picture @270k scale?). Anyway, works now
I used this resize tool: http://www.faststone.org/FSResizerDetail.htm
thanks you everbody for the help, I might've given up otherwise :)
I'll probably write up a small tutorial some time for bulk data & image processing using Gnuplot and LaTeX. Next up is the Python-Script to generate the LaTeX-Code for all the pictures (~150) :)
EDIT: in case somebody is interested, this is the python-code I used for generating lots and lots of LaTeX-code:
f = open('Hex06.tex', 'w')
hex = 'Hex06'
print('\n')
print('writing Hex06.tex .....\n')
for field in ['03_2h3h','03_23','04_6h5','04_36h','04_55h','06_55h','07_6h5','07_44h','07_55h','07_66h','06_6h5','07_5hh4','07_34','09_13','16_12','08_16']:
if(field == '03_2h3h'):seg = '0'
if(field == '03_23'):seg = '0'
if(field == '04_6h5'):seg = '0'
if(field == '04_36h'):seg = '0'
if(field == '04_55h'):seg = '0'
if(field == '06_55h'):seg = '0'
if(field == '07_6h5'):seg = '0'
if(field == '07_44h'):seg = '0'
if(field == '07_55h'):seg = '0'
if(field == '07_66h'):seg = '0'
if(field == '06_6h5'):seg = '1'
if(field == '07_5hh4'):seg = '1'
if(field == '07_34'):seg = '1'
if(field == '09_13'):seg = '1'
if(field == '16_12'):seg = '1'
if(field == '08_16'):seg = '2'
f.write('\n')
f.write('\\begin{figure}[!htbp]\n')
f.write('\centering\n')
f.write('\\fbox{\includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_+15V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_0V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_-15V.png}\n')
f.write('}\n')
f.write('\n')
f.write('\\fbox{\includegraphics[scale = 1]{' + hex + '/SEM-pics/resized/' + hex + '-done_field'+field+'.png}\n')
f.write('\\textbf{{\Huge '+hex+' '+seg+'-Au-Segments}}}')
f.write('\n')
f.write('\\fbox{\includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_+2V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_0V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_-2V.png}\n')
f.write(' }\n')
f.write('\end{figure}\n')
f.write('\\newpage\n')
f.write('\n')
f.close()
print('done with Hex06.tex, starting Hex07.tex.....\n')
f = open('Hex07.tex', 'w')
hex = 'Hex07'
for field in ['06_41','06_56','08_4h5h','08_45','11_16','14_21','14_66h','18_6h1h','06_15','09_23','18_16h','14_16']:
if(field == '06_41'):seg = '0'
if(field == '06_56'):seg = '0'
if(field == '08_4h5h'):seg = '0'
if(field == '08_45'):seg = '0'
if(field == '11_16'):seg = '0'
if(field == '14_21'):seg = '0'
if(field == '14_66h'):seg = '0'
if(field == '18_6h1h'):seg = '0'
if(field == '06_15'):seg = '1'
if(field == '09_23'):seg = '1'
if(field == '18_16h'):seg = '1'
if(field == '14_16'):seg = '2'
f.write('\n')
f.write('\\begin{figure}[!htbp]\n')
f.write('\centering\n')
f.write('\\fbox{\includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_+15V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_0V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_-15V.png}\n')
f.write('}\n')
f.write('\n')
f.write('\\fbox{\includegraphics[scale = 1]{' + hex + '/SEM-pics/resized/' + hex + '_field'+field+'.png}\n')
f.write('\\textbf{{\Huge '+hex+' '+seg+'-Ni-Segments}}}')
f.write('\n')
f.write('\\fbox{\includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_+2V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_0V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_-2V.png}\n')
f.write(' }\n')
f.write('\end{figure}\n')
f.write('\\newpage\n')
f.write('\n')
f.close()
print('done with Hex07.tex, starting Hex10.tex.....\n')
f = open('Hex10.tex', 'w')
hex = 'Hex10'
for field in ['01_1h2','01_6h6','01_13','01_55h','02_55h','02_66h','01_5h6h','01_21','02_6h5','02_34','04_45','05_1h3','07_61','08_4h3','08_32','09_64','12_1h6','16_63']:
if(field == '01_1h2'):seg = '0'
if(field == '01_6h6'):seg = '0'
if(field == '01_13'):seg = '0'
if(field == '01_55h'):seg = '0'
if(field == '02_55h'):seg = '0'
if(field == '02_66h'):seg = '0'
if(field == '01_5h6h'):seg = '1'
if(field == '01_21'):seg = '1'
if(field == '02_6h5'):seg = '1'
if(field == '02_34'):seg = '1'
if(field == '04_45'):seg = '1'
if(field == '05_1h3'):seg = '1'
if(field == '07_61'):seg = '1'
if(field == '08_4h3'):seg = '1'
if(field == '08_32'):seg = '1'
if(field == '09_64'):seg = '1'
if(field == '12_1h6'):seg = '1'
if(field == '16_63'):seg = '1'
f.write('\n')
f.write('\\begin{figure}[!htbp]\n')
f.write('\centering\n')
f.write('\\fbox{\includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_+15V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_0V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_UI_all-currents_' + hex + '_'+seg+'seg_field'+field+'_-15V.png}\n')
f.write('}\n')
f.write('\n')
f.write('\\fbox{\includegraphics[scale = 1]{' + hex + '/SEM-pics/resized/' + hex + '_Au-seg_field'+field+'.png}\n')
f.write('\\textbf{{\Huge '+hex+' '+seg+'-Au-Segments}}}')
f.write('\n')
f.write('\\fbox{\includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_+2V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_0V.png}\n')
f.write(' \includegraphics[scale = 0.7]{' + hex + '/2P_TR_all-currents_' + hex + '_'+seg+'seg_field'+field+'_-2V.png}\n')
f.write(' }\n')
f.write('\end{figure}\n')
f.write('\\newpage\n')
f.write('\n')
f.close()
print('done with Hex10.tex\n')
print('\n')
print('pleasure to do business with you\n')
print('see you next time\n')
print('\n')

subfigurepackage is deprecated I think. See https://tex.stackexchange.com/questions/144782/subfigure-and-subfig-packages-deprecated. Better to usesubfigorsubcaption. – Troy Apr 25 '17 at 13:59