Slideshows work best on home pages in one of the home page layouts.
Photos should be 1900px by 500px and optimized for use on the web. Find out more in our Photo Best Practices section.
Always put in a title (it is the alt text) and if you use the caption feature, format the text using the styles in the web part ribbon.
Slideshows on internal pages using the Three Column or Two Column layouts are not optimal under most circumstances.