We do not resize the images sent up to 1024 pixels on the longest side (our scaling for larger images is identical to that used in Photoshop).
After applying the Copyright bar, returned to recording with 100% quality in our tests comparing the pixels do not show visible signs of alteration.
The image below has not been resized or edited in any way is a crop of the original 100%.
The image on the right has a conversion to jpg. ( Original 16-bit Photoshop => jpg )
The left image has three conversions to jpg. (Original 16-bit Photoshop => jpg; Upload Site => jpg; Photoshop => jpg)
If you use a workspace (profile) should save your images with the option Preserve embedded profile, so everyone can see images with the same saturation, contrast and density. We convert all profiles for sRGB used on the net, so everyone can see the same images in all browsers.