ES, good question. David's photo is very large 2592 x 1456 pixels and about 1.5MB. I think, but I'm not certain that's why it appears so large. Reducing it in size before linking to it should make it display better, but that requires using a photo editing program or some other bit of software. Here I've reduced it to 1366 x 768 pixels and it still looks too large.
The other trick requires some knowledge of the MyCode—the code used by the forum software to display images. See the bit on photo size in the forum's help section.