Some online photo-hosting sites restrict the size of photos they will host. There are at least two kinds of resizing. Either the dimensions are too large or the storage space required is deemed too big.
Photorazor is a free, small (only about 1.5 megs), brilliant piece of software that will re-size and optimize for the web your photos individually or a whole folder at a time. You can choose the size and degree of compression. It is good netiquette to keep your image file sizes as small as is consistent with good reproduction, usually less than 100 kbs.
Here's how to resize your image with MS Paint.
Open MS Paint.
Open your photo.
Click on Image then click on Stretch/skew in the drop-down menu.
Choose a percentage to stretch the photo by1). Make sure you choose the same percentage for the horizontal and the vertical stretch.
Click OK and view the new photo size.
If you don't like it, UNDO your change with Ctrl Z and repeat the steps choosing a different percentage.
The size of your photo can be changed simply by changing the type of file that it's stored as. For example, a .bmp will take more space than a .jpg
Open your .bmp file with MS Paint.
Click on Save as and choose .jpg in the Save as type drop-down menu.
Click on Save and your photo should now be a lot smaller.