The general rule is that you need permission to use anything that anyone else created -- images, text, video, etc. -- regardless of where you find it. There are narrow exceptions if, for example, you're using the images for commentary (what's known as "fair use") or if the image has a creative commons (or other freeware) license. If you're planning to go into the world of online media, copyright infringement is a huge (and costly) issue to run afoul of. Align yourself with an intellectual property attorney -- even if it's to get the basic consultations -- so that you can steer clear of the pitfalls.
Creating a MAP will take no more than an hour of your time every month and will keep the lines of communication open, ensuring relationships with investors remain strong, and ultimately helping early-stage startups succeed.