Have been set to the largest preset size. Images should always be saved and uploaded, not inserted with HTML. Be aware that images must be sized similarly (width should be exactly the same in the instance below) to look uniform.
This is an example of a Google+ photo album slideshow. All slideshows must be made from albums in your G+ profile.
Always insert a blank line above a horizontal rule.
Maybe you want to show images side by side. In this case, choose a page layout that has columns and adjust the image sizes properly so that they're the same width. You can use www.pixlr.com to edit photos for free.
Be sure to remove links from images in this instance. Otherwise the formatting will be thrown off. Highlight images and center them on the page to make them a little more uniform.