Hope this helps JPEG being lossy, every time you load, then save, a separate JPEG algorithm is applied again. I believe the default for Photoshop is High quality, which an 8 on their dialog. So if you have an original JPEG that was originally saved as a low or medium quality (say a 4-6 on the Photoshop dialog), if you then open that in Photoshop, and go with the default "High/8" quality save, then the JPEG algorithm is applied on the perceptual image, meaning you saved a lower quality perceptual image at a higher quality algorithm's amount of data. This is a major reason that I've moved away from JPEG. If JPEG is required I always try to start with either a RAW, BMP, TIFF, or PNG image, and then save off a JPEG version from that, then if I need to make any changes I go back to the full "original" [lossless] format, make the changes then save the JPEG again. I try to never edit an image that is already saved as JPEG, because you're always going to lose a small amount of quality (mostly the JPEG algorithm is good enough that the loss of quality isn't perceptual, but the file size can change none-the-less).
Is there any known limit for the size of an app uploaded and for the GBs assigned to a runtime?
Does that help The size of the application is limited to 1GB as mentioned here. The Memory allocation is limited to 8GB per app, you can see this when you try to allocate more than 8GB in the Bluemix UI as it either resets to 8GB or if, using the toggle, doesn't allow you above 8GB.
PHP How to limit users to a specific number of files that can be uploaded