Process all of those images before you upload them to your site. Here is a photoshop script to do that. File -> Scripts -> Browse

resizeImages.jsx

// A Photoshop script to process a folder of images. It creates 3 versions of each image
// e.g. some-image-name.jpg will produce
//    * some-image-name-full.jpg
//    * some-image-name-mobile.jpg
//    * some-image-name-thumbnail.jpg

var IMAGE_QUALITY = 5;
var VALID_IMAGE_TYPES = Array( "jpg", "png", "gif");

main();

function main(){
	// Prompts user to select folder
	var startFolderPath = "~"
	var inputFolder = Folder(startFolderPath).selectDlg("Select a folder to process");

	// Get's all jpg files in the selected folder
	if (inputFolder == null){
		//if nothing selected, exit script
		return;
	}
	var fileList = inputFolder.getFiles();
	processImages(fileList);
}

function processImages(fileList){
	// Iterate through files in the selected folder
	for(var i=0; i<fileList.length; i++) {
		var file = fileList[i];
		if (isValidFile(file)) {
			open(fileList[i]);
			var doc = app.activeDocument
			var fileName = doc.name.replace(/\.[^\.]+$/, '');

			// Save main image at correct quality
			saveImage(doc, fileName + '-full');

			// Resize and crop for mobile
			var height = 264; var width = 505; var top = 20;
			doc.resizeImage(width);
			doc.crop(new Array(0, top, doc.width,height + top), 0, width, height)
			saveImage(doc, fileName + '-mobile');


			// Resize for thumbnail
			var thumbW = 163; var thumbH = 78;
			doc.resizeImage(thumbW, thumbH);
			saveImage(doc, fileName + '-thumbnail');

			// all done!
			doc.close(SaveOptions.DONOTSAVECHANGES);
		}
	}
}

// Checks to make sure it is actually a file, that it isn't hidden, and that it is a valid file type
function isValidFile(file){
	if(file instanceof File && !file.hidden && isValidFileType(file.toString())){
		return true;
	}
	return false;
}

function isValidFileType(fileName){
	// make sure it has a file extension
	var lastDot = fileName.toString().lastIndexOf( "." );
	if ( lastDot == -1 ) {
		return false;
	}

	// check file types
	var extension = fileName.substr( lastDot + 1, fileName.length - lastDot ).toLowerCase();
	for (var i = 0; i < VALID_IMAGE_TYPES.length; i++ ) {
		if ( extension == VALID_IMAGE_TYPES[i] ) {
			return true;
		}
	}
	return false;
}

function saveImage(doc, fileName){
	var saveOptions = new JPEGSaveOptions();
    saveOptions.embedColorProfile = true;
    saveOptions.formatOptions = FormatOptions.STANDARDBASELINE;
    saveOptions.matte = MatteType.NONE;
    saveOptions.quality = IMAGE_QUALITY;

	var saveFile = new File(decodeURI(app.activeDocument.path) + '/' + fileName + '.jpg');

	doc.saveAs( saveFile, saveOptions, true );
}