The larger the image, the more space it takes on the server and the longer it takes for viewers to see. It is best to prepare graphics before inserting them. With Photoshop use the "Save for Web" command. The idea is to reduce the memory size, not necessarily the image size. The example here is for JPG compression. If you want GIF compression the steps are the same; just click on the arrow to the right of jpg and choose gif.

When you go to FILE > Save for Web... this dialog box will appear. On the left is the original image and the amount of K used in it's present state. On the right is the compressed image and it's size IF you leave the Quality or Compression at it's present state. Sometimes that is fine and sometimes you may wish for higher quality because the image is too blured (or too compressed). Change the quality from low to medium or even to high. Each time ,look at the image on the right and the amount of K that image will uses. Often it is a choice of quality or size and you have to comprimise. Choose what looks good to you at the smallest memory size.

After the amount of compression is chosen, click OK, and complete the save by choosing where to save the image.