Add image_8 graphic

NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md

@@ -915,7 +915,7 @@ Example:
 
 > 4 has density .75 and B has density 1.75 in one place. From the first graph, the double exposure from positives has density about 1.0 in that place.
 
-**![Graphics depicting DOUBLE EXPOSURE FROM POS'S, BIPACK (1.0 COMPENS) DOUBLE EXPOSURE FROM NEGS and GAMMA 1/2 BIPACK](#)**
+**![Graphics depicting DOUBLE EXPOSURE FROM POS'S, BIPACK (1.0 COMPENS) DOUBLE EXPOSURE FROM NEGS and GAMMA 1/2 BIPACK](img/image_8.jpg)**
 
 For a double exposure it doesn't matter which exposure is first, or what time separates the two.
 In some multi-head optical printers, using a beam-splitter, the two exposures are simultaneous.

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@@ -1172,7 +1172,7 @@
 <blockquote>
 <p>4 has density .75 and B has density 1.75 in one place. From the first graph, the double exposure from positives has density about 1.0 in that place.</p>
 </blockquote>
-<p><strong><img src="#" alt="Graphics depicting DOUBLE EXPOSURE FROM POS’S, BIPACK (1.0 COMPENS) DOUBLE EXPOSURE FROM NEGS and GAMMA 1/2 BIPACK" /></strong></p>
+<p><strong><img src="../img/image_8.svg" alt="Graphics depicting DOUBLE EXPOSURE FROM POS’S, BIPACK (1.0 COMPENS) DOUBLE EXPOSURE FROM NEGS and GAMMA 1/2 BIPACK" /></strong></p>
 <p>For a double exposure it doesn’t matter which exposure is first, or what time separates the two. In some multi-head optical printers, using a beam-splitter, the two exposures are simultaneous. Either way, the two films can be independently adjusted for exposure, filtered, etc.</p>
 <p>For a bipack it doesn’t matter which film is in front. Also the two may be optically instead of mechanically bipacked. In some multi-head optical printers the films are in separate gates, ones projection becoming the other’s illumination. In a simple printer one film may be in the gate and the other in the camera, in front of the print film. Any way, the two films ehare one exposure adjustment and filtration.</p>
 <p>When films will be physically bipacked they should first be wiped with a lubricating film cleaner. This is good practice for all optical printing when delicate originals receive heavy handling.</p>