• Make sure you are labeling your vacation rental images with searchable keywords (eg. vacation-rental-villa-las-terrenas.jpg) as search engines scan the text, that is associated with your images.
• Don’t forget to use „alt tags“ (alternative text), brief keywords that relevantly describe your vacation rental images.
• Watch your image dimensions as load time is important for your SEO (large photos cause lengthy loading times: may negatively impact your google ranking and frustrate visitors). Research the optimal dimensions for your website provider and stick to them.
• Keep an eye on image compression (file size should be below 100 kb).
• Use the right file type (JPEG for photos showcasing your vacation rental; PNG for your company logo and graphics; GIF for animated images) …

(Source: via @Lodgify – http://blog.lodgify.com/vacation-rental-website-optimize-images )