I just want to briefly list some helpful links to image services that I came across the other day.
Flaticon is the largest search engine of free icons in the world.
Giphy is a website that provides lots of gifs. There also exists a public API that allows to search for gifs and embed their url in your website.
Public API: http://api.giphy.com/v1/gifs/search?api_key=dc6zaTOxFJmzC&limit=1&q=yourSearchTerm
Placeimg provides placeholder images for your project in progress. Custom URLs generate placeholder pictures in various sizes with categories and effects.