Free image libraries
https://unsplash.com
https://gratisography.com
https://www.pexels.com
Free image embedding (suitable for content, not featured image)
https://www.gettyimages.co.uk/
Free online image editing
https://www.fotor.com/app.html#!module/basic/tool/BasicEdits
https://resizeimage.net/
Key 16:9 image dimensions
16 x 9
32 x 18
64 x 36
96 x 54
128 x 72
160 x 90
192 x 108
224 x 126
256 x 144
288 x 162
320 x 180
352 x 198
384 x 216
416 x 234
448 x 252
480 x 270
512 x 288
544 x 306
560 x 315
576 x 324
608 x 342
640 x 360
656 x 369
672 x 378
704 x 396
720 x 405
736 x 414
768 x 432
800 x 450
816 x 459
832 x 468
864 x 486
896 x 504
928 x 522
1184 x 666