One of the clues from the crossword puzzle tells us that "The third digits are what the pictures have in common." From a post by Bernard, we can assume that we are looking only at the four images that have no relevance to any of the articles, in that particular issue. However, here are all the pictures from Volume 01 Issue 01 of the Curios & Conundrums newsletter.
"Cross" - Admittedly this is a stretch. But if the commonality is the cross, then the third set of digits could be found by multiplying (or possibly adding?) the other two sets of digits.
- Page 2 - The communist article shows the man on the right being "cross" (angry) at the man on the left.
- Page 2 - The crow/raven is walking "across" the page.
- Page 2 - The Celtic-knot-like design forming the moon and the stars features several crossing lines.
- Page 3 - The swimsuits are a "cross" between 1910s and 1930s swimsuit designs.
- Page 4 - The Giant's Causeway is a "crossing" between Ireland and Scotland.
- Page 5 - The crown features a cross.
- Page 5 - The alerion's tail resembles a cross.
- Page 6 - The crosier features a cross.
- Page 6 - The occulizer has a cross on its rubber bulb.
- Page 7 - The clue was found in a "cross" word puzzle.