Those photos are not much better. I measured one after displaying it at IT'S full resolution and that was 640 H x 480 V pixels. This is probably a combination of a cell phone's settings (their screens are lower resolution than even that) and Flickr which has it's own processing and limits on the resolution.
Why can people not post photos with a resolution that takes advantage of the modern displays on DESK TOP computers while not exceeding the horizontal width of the smallest of those screens. It is not hard to do.
1. Open the photo in Microsoft Paint or the Apple equivalent. Paint is free and included with all Windows installations.
2. Change the resolution IN PIXELS to a horizontal setting of 800 to 1000 pixels. Let the vertical resolution follow that horizontal setting to keep the aspect ration the same.
3. Save that photo in it's new resolution.
4. Just use that new photo and upload to THIS BB's image hosting service. The BB software will preserve a horizontal resolution of 800 to 1000 pixels. If you upload a photo with a greater horizontal pixel count, it may reduce it according to it's own rules. I routinely upload pictures both here and on other BBs with 800 horizontal pixels and they are always displayed INSIDE THE POSTS with that resolution. No clicking around is needed.
Just use this BB's image hosting and forget the others, like Flickr.
So much is said about not wasting the time of the members here with posts about amateur or home shop equipment. But what about wasting our time with photos that do not convey the information needed to answer a question. Every thumbnail is an instant time waster. I hate thumbnails.
Example of the above with 800 pixel horizontal resolution:
And another example with 1000 pixel horizontal resolution. The BB apparently reduced it to 860 pixel horizontal resolution. Perhaps that is the limit.
Notice how you can see details in them? And they are right there, in the post. No clicking to try to see them.
PS: Don't tell me your cell phone can not change the resolution of a photo. I have a real cheap, Android phone and even it can. I may not have used yours, but I am willing to bet it is a lot better than mine and that it CAN easily change the resolution of a photo.