Thanks for your question and sorry I've not updated you before now.
Our tech guy looked into this, but it appears that Tapatalk (who provide the software we use for the app) have removed this resizing feature, and I'm afraid there's currently no way for us to re-enable it. It is possible that the feature may return in a later update of the app though.
We do what we can to respond to members' feedback about features on TP, but what we can change is sometimes limited by the options that both the forum software and the app software offer us.
Sorry Jeany and I hope that won't put you off using the app,
We've made a fix to this issue and it will be included in next release.
For your quick solution, you can set your forum upload size to 1024x1024, or enable forum resize image in: "AdminCP->vBulletin Options->Message Attachment Options->Resize Images"
I like the app but (and I feel a bit silly admitting it) I can't work out how to log out! I've been logged on for ages now - I suppose it doesn't matter, but would like to know - bet it's something really simple!