This is kind of hard to explain but I'll try.
The "size" of these photos has nothing to do with the physical dimensions. The size is determined by the number of "dots" that make up the photo. The more dots, the higher the resolution. That means you could blow the photo up really big, and still have it be clear. A high resolution photo might be well in excess of 600 dots per inch. (pixels in computer terms)
Here's the rub. The highest resolution a computer screen can display is about 96 dots per inch. Anything above that is waste.
Photo bucket has reduced the resolution of your photo. The limit here is 2,194,304. The photo above is 174,515. Rather than crop the photo, just reduce the resolution.
Endeavor to persevere.