Recommended height and width for promoted links background images

Question

I want to create some images to be defined as background images for promoted links. However, I did not find any articles or documentation that define the recommended height and width for these background images. Should I use specific dimensions or it does not matter?

Edit

now i define the following custom style as mentioned on the link you provide link

<style type="text/css">
            div.ms-promlink-body {
                height: 100px;
            }

            div.ms-tileview-tile-root {
                height: 110px !important;
                width: 110px !important;
            }

            div.ms-tileview-tile-content, div.ms-tileview-tile-detailsBox,  div.ms-tileview-tile-content > a > div > span {
                height: 100px !important;
                width: 100px !important;
            }

            div.ms-tileview-tile-content > a > div > img {
                max-width: 100%;
                width: 100% !important;
            }

            ul.ms-tileview-tile-detailsListMedium {
                height: 100px;
                padding: 0;
            }

            li.ms-tileview-tile-descriptionMedium {
                font-size: 11px;
                line-height: 16px;
            }

            div.ms-tileview-tile-titleTextMediumExpanded, div.ms-tileview-tile-titleTextLargeCollapsed, div.ms-tileview-tile-titleTextLargeExpanded {
                padding: 3px;
            }

            div.ms-tileview-tile-titleTextMediumCollapsed {
                background: none repeat scroll 0 0 #002E4F;
                font-size: 12px;
                line-height: 16px;
                min-height: 36px;
                min-width: 97px;
                padding-left: 3px;
                position: absolute;
                top: -36px;
            }

            li.ms-tileview-tile-descriptionMedium {
                font-size: 11px;
                line-height: 14px;
                padding: 3px;
            }

</style>

this have modify the width and height for the prompted links, but it did not modify the tiles images which now became out of layout since only part of the images will be shown as follow:-

Answer 1

The promoted links default size is 150x150 pixel. But you can always have bigger/smaller pictures and then manipulate the CSS for the promoted links if you want bigger/smaller tiles.

Change the default tile size in Sharepoint 2013

Edit

Add this to the bottom of the CSS before closing the style tag.

.ms-tileview-tile-content img {
    width:100px!important;
    height:100px!important;
} 

This won't apply on the "Getting started" promoted link webpart as it is using just one picture and uses CSS to position it.

In the example below, my pictures are sizes 150x150px so they won't look good being scaled down to 100px. Better to create the pictures/icons in the size that you want your tiles to be in the first place.