@franceskeeley
A few quick pointers:
A good rule of thumb for Weebly is to upload an image that's the same size as it can be displayed. The majority of webpage body, Weebly included, are around 900-1200px wide, so you're on the right track with your sizing x column estimates. If you upload an image that's much larger than its display size (in px and/or kb/mb) it will get compressed by Weebly and that often leads to noticeable reductions in image quality. If your viewers are using mobile devices you can get away with much more in terms of image quality, if they're using desktop monitors, reduced image quality will quickly become obvious. If images are important for your website, build with larger monitors in mind (which you seem to be doing by taking into account the page width). That said, if you're going to use a lightbox or some other method where you click on an image to view a larger version, you will need to upload the larger version.
As for sizing images - large images (like those from an SLR) are best reduced using bicubic sharper algorithms but watch out for potential oversharpening. If that's occurring or you're using lower resolution images, see if plain bicubic works better. I would advise against using free online image reduction tools, some are dire, others so-so, occasionally OK. They aren't really meant for maintaining high image quality, more for enabling quick load times. Software like Photoshop/Lightroom and Gimp offer the best algorithms by far. If you don't want to pay for Photoshop/Lightroom, Gimp is free but quite difficult for the novice to learn quickly. Irfanview is also a free download, it's easier to use and is very good quality software. The batch resizer is particularly good. Last thing, always upload images in sRGB colour space, not RGB, even for black and white images (and don't use grayscale, less tonal range).
Gary
