The upper limit on the size of files that can be attached to the wiki is 500Kb (about 500,000 bytes). For a time, it was set to 5Mb (about 5,000,000 bytes), but this has led to the creation of pages that contain so many very large images that the pages take much, much too long to appear on-screen. Images that will be displayed on-screen with a width of from 200 to 300 pixels, as most typically are, should NOT be uploaded with a dimension of 2800×1900px, as some 1.5Mb picture files have been. Using wiki-code to restrict the size at which such an image will display on-screen doesn’t spare the reader’s browser from having to download the entire file. Even one such file will slow down the browser’s rendering of the page. A page-full is likely to crash the browser.
If you’re using a mac, you almost certainly have a built-in image-resizing utility on your computer. If you’re using windows, the software that came with your camera probably has such a feature, or you can use Microsoft’s ImageResizer powertoy. Mac or Windows, you can use this online resizer.
Look at the (first four) pictures on WatershedWisdom.HomePage. Click on one, and your browser will display a larger version of that picture (the larger versions of the horizontally-oriented pictures are about 1,000px wide; all are well under 200Kb). The page makes use of two versions of each image. The version that’s displayed is a thumbnail file (under 20Kb), with a larger dimension (height or width depending on the picture’s orientation) of 200px. It’s set on the page as a link to the larger version, which was uploaded as a second file.