IPB still have not really solved the situation as they do not understand the users needs. If the thumbnail image size is set to 150x150 - so posts can display lots of small efficient thumbnails quickly to thousands of visitors, they are saying the lightbox will display the same image - Which is going to look sh$thouse. The light box should probably display the larger of the images (and browser scale it down to fit the lightbox.. this would be the better option for the light box.
I cannot believe that there is no thumbnail image processing... This topic shouldn't be up for discussion! What IPB are saying is if someone uploads 10x 2meg image files, the board can **display** them 150x150 (or whatever setting has been chosen by admin), but the poor end user needs to download 20 meg of data to get that view. The server has to serve it and the board administrator has to pay for it. Mobile users may as well give up, because they will be paying for it to. This is a HUGE mistake by you guys that needs fixing. Images should be able to be uploaded by OP in what ever size they like (with a max meg setting set by admins if required) Images should then be processed - a thumbnail image should be created to whatever size has been set by admin.
Optionally the original image should be resized down to dimensions set by the admin - So when end users view the 'large' version its either the original image or a smaller version if set by the admin.
So for a real life example: OP uploads a 100 megapixel image taken with a D1000000 camera and its 85meg. The system accepts the upload, but then scales it down to 1500x1500 for storage A thumbnail is also created and stored at 150x 150 and is used for thumbnails. When an end user views the page, the 150x150 image is loaded by the browser. When the end user clicks the thumbnail the 1500 x 1500 image is loaded by the browser. The admin is happy because he hasn't served an 85 meg image, and the end user is happy because they can see a decent size version when required and the original poster is happy because he was able to upload his image without resizing it first.