First, I believe most everyone is aware that images can not be uploaded directly to the Country Plans Forum server; images must be hosted elsewhere and linked to in the message posts.
Next, let it be noted that the forum software will display images at a maximum width of 1024 pixels and a maximum height of 1024 pixels. If a linked to image is larger than either dimension the forum software will display the image but within the constraints of the 1024 x 1024 maximum size. However, if the image stored on photobucket.com, or other location, is larger than the 1024 x 1024 pixel size it will still take longer to be downloaded to any computer viewing the message than would be if the stored image was smaller.
This may not seem important to those with fast DSL or Cable connections. However, there are members with slower connections. Any topic that has many images that are in large file sizes will "take forever" to load the images. Many times those members may simply decide to ignore topics that are heavy with large file images.
When we speak of image sizes there are actually two things to consider; the actual image size in pixels and the image file size. Image hosting services like photobucket can be set by the individual to limit the image sizes. Mine is set to limit the image size to 1024 x 768 pixels. This means that when I select an image on my computer that is 3264 x 2448 with a file size of 2.72 MB, the photobucket software reduces the image to 1024 x 768 with a file size of 923 KB after it is uploaded. That's a better file size than the original. However it is still huge for forum use. A topic with a dozen or two images of that size will take a long time to completely download to a viewer on a slower connection.
On the subject of image sizes and other folks computers also note that there are some users with older computers and smaller monitor displays. For these folks even a 1024 x 768 image size can overflow their screen. For that reason I will frequently downsize my images meant for forum posting to 800 x 600.
By resizing images on your own computer and saving them as JPEG's with a high compression rate, that file can be dropped down to 100 KB, or even smaller. That resized smaller file can then be uploaded to the image host service. While such an image file may not make a high quality print on most common size monitors the quality will still be difficult to distinguish from the larger image file, larger file size. And best of all those with slower connections may actually view your topics and posts.
There are many image editing programs in use. With something like Photoshop the image quality can be selected when performing a "save as" operation. I find a Photoshop quality setting of 5 still provides images of good quality for the internet. Similarly I have also have Paint Shop Pro and it uses percentage settings. A compression ratio of 60% also provides decent internet images. These methods can easily get an image down to approximately 100 KB in file size.