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Using a CSS only approach, add the following CSS inside the content editor webpart or add it to your custom css.

<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>

For OOTB sharepoint images (sprite images that you get by default), you'd have to adjust the positioning for each images. For your own images, the above code should do the trick. The code is for 100x100 size.