We are currently redesigning our website http://www.aljoufilaw.com/ar/ and we are inserting photos in the sub-pages of the site.

What is the best format to use that would render the photo in high quality and high resolution?

Does increasing the resolution of the photo in Photoshop by going to image>image size>resolution, then set the resolution to 1200 for example, increase the quality of the photo?

We really appreciate your expert advice on this. Thanks.