So you have your Flicker, your Instagram, Facebook, Pinterest. The image sizes are different for your G+ profile as compared to your Twitter header. I make these images every day and I have to figure them out every time! Luckily and thankfully the folks at Constant Contact have created a social media image guide cheat sheet to help us keep them all sorted out. Honestly, I am the first person to scrawl an image size down for “future reference” and promptly throw it away accidentally when I clean up my work area. This is a great resource to bookmark for future reference! The article has more information on how to resize and interesting facts about the “why” if you are interested. Personally, I always find myself more engaged with a nice image that looks “right” on a page or an article.
For more information, resizing resources and the link to the article head on over to the Constant Contact Blog post and get the 2014 Social Media Image Size Cheat Sheet.