If you would like to open an image in a new tab right from the search result page, you have two easy options.
Using the keyboard shortcut:
Simply hold the ctrl and the alt/option key and left click on the image you would like to open in a new tab. The image will open in a new tab next to the one you are currently using Ecosia with.
Using your mouse:
Right click on the image and choose "open image in new tab". However, some browsers don't offer this function, so the keyboard shortcut probably is the easiest to go by.