One thing you could do sometimes is in addition to the 800x600 images you could also post links to the full size images so people can view them if they want to.
That's right and if it's linked in to a post from somewhere else on the net like an image hosting site then it will show as whatever size it is. I use Photobucket for all the images I post, it has a built in editor and is easy to resize your photos so I would recommend that, they give you enough space for free and you can buy more if you want.
For those who don't use a tablet yet and don't know what the issue is here I will explain. On your laptop or windows computer a thread will display normally and you get to the huge photo, you then slide your screen back and forth to view the whole thing. Well some tablets now have higher resolution than your computer screen and photos look better and have more detail than when viewed on your computer screen, so those huge photos can be viewed all on screen without having to slide the screen back and forth. The problem is that you get the opposite problem you get on the windows computer. When I view a thread with one or more huge photos those photos show perfectly all on screen while the rest of the thread shrinks to a tiny size!
More and more people will be using tablets instead of laptops and plenty of people can't read fine print and may also not have their computer screens set to the highest resolution, so everyone please keep this in mind when posting photos.
Alan