If you are sharing photos which are relevant to the subject, does that really count as spam?

No, it doesn't, but if you post hundreds of them it most likely is!

is it not OK for your 'partner' to up-vote this additional content?

Oh yes, that's generally fine, but again, hundreds of times over and exclusively so, it is obviously nothing but farming for money then!

On a similar note, my partner @osmosis signed up recently, and I have to beg her to vote for my content at times! Yes, i will re-steem and up-vote some of her content/comments, but i think we will escape action (following your potential visit) now I have added this :)

As I've noted in the case: "Naturally @kiporen212 and @kimor upvoted and resteemed each other's content, and back then, there was absolutely nothing wrong with that." That is absolutely not a problem. Only when you start posting spam exclusively and just for reciprocal upvoting, like our culprits do in this case, then I'd argue it is clearly an offense!