Here is a website that provides a free online social banner maker. Create vertical, horizontal, rectangular, square and custom sized banners that can be used on social media platforms. Use multiple images and text to make an info-graphic.
I was especially looking for help with making images that stand out on Pinterest. Here is a link to another site that provides the proper dimensions needed for best displaying in Pinterest boards, the feed view, and expanded pins. Click on >>> Pinterest Style Guide
Fotor Banner Maker is where you can create your own banners in all sizes for free; you can either generate your banner from scratch or customize from pre-designed banners by changing the wording, overlays and pictures. read more at fotor.com