I don’t know the answer either, but I read somewhere that the forum/software doesn’t allocate space to store photos and that is why you need to use a photo service like Photobucket, Imageshack, etc. The images are stored on a third party site and then linked into the forum pages as you view a page.
From my personal observation, it appears the beemaster forum will retrieve your photos from the third party site (via the [img] tag you add to your post) and resize them to fit the forum pages. It looks likes Beemaster resizes the photo so they don’t exceed about 600 pixels wide. You can probably post whatever size of photo the third party site will allow, but the extra resolution in those big photos just wastes bandwidth as Kathy says. It takes time for the bee master site to pull down a large photo from a third party photo site and resize it. That shows up as a delay in seeing the photo in the forum.
Most digital cameras shoot photos with sizes of at least 2256 x 1496 pixels, most even bigger. That’s way bigger than peoples monitor (1920 x 1080) and wastes bandwidth when being viewed on a monitor (like viewing a forum). The raw big photos will work, but they just slow down the works.
What I do, is resize my raw photos down to 800 to 1000 pixels wide before uploading them to photobucket. That size can be uploaded and downloaded much quicker and still has plenty of resolution to show detail. Of course I resize a copy of my original raw file and keep the original full sized photo on my computer.