Following will help you in learning about re-sizing pictures:
"5. ... One has to re-size one's pictures to say max. upto 800 by 600 pixels at 72 DPI with quality settings of say 5 to 10 to bring it upto a max. of 150 KB in Photoshop as per group guidelines for posting. Links are to be avoided as far as possible as attachments are allowed. To re-size in Microsoft Photo-editor, which is available in most Window based computers: Open your picture in Microsoft Photo Editor. Select Image--> Resize & select width of say 800 pixels under width units (height sets itself), Click on OK. Select File--> Save as, choose file name as … & click on save button. Now file is ready for web use. It is much reduced in size. If, it’s still more than 150 KB, it can be reduced within 150 Kb by selected width of say 700 pixels or less instead of 800 pixels. Similar procedure can be followed in other picture processing software. Pl. also see a few relevant links here: https://sites.google.com/site/efloraofindia/miscellanea/for-members-information/re-sizing-pictures"