Image Editing Tools and Guidelines
Graphics need to be properly sized if they are to be easily visible to the individuals viewing your documents. The two main elements of image size are dimensions (measured in pixels) and file size (measured in kilobytes or megabytes). These elements can be independent of each other. A small image could be a large file and a large image could be a small file. When it comes to viewing an embedded image on a web page or as a document, a small image which is a large file contains useless information which slows the loading process. Such files should be compressed, and may need to be resized to smaller dimensions.
Image dimensions are a matter of appropriateness to the page in which the image appears, so there are no absolute guides for maximum and minimum dimensions. We recommend that the dimensions of the largest image attachment to a document be no more than 600 pixels vertically and 800 pixels horizontally, as this will open conveniently on a computer monitor.
100 K is an adequate size for most embedded graphic files, and in most cases embedded graphic files should not be larger than 200 K. Graphic files attached to a document can be larger than 200 K, depending on how they will be used or viewed.
Your computer or digital camera probably came with graphics editing software. For example, an excellent tool on PCs is the Microsoft Office Picture Manager. If you use this software you simply need to open your graphic file in Picture Manager, select Picture on the top bar, then select Compress, then select Web Pages and then OK. The software will resize and compress the image. Save it and insert it in your document.
If you do not have MS Picture Manager, a free and easy to use tool is IrfanView, which can be downloaded here.