How can i change the image size on disk ... not the image size

I resize me images to one size 64x64. but when i need to use them i found that the size on disk is not same for all images. my network doesn't work with this issue. how can i do resizing my images for both the normal size and the size on the disk. Thanks

[Dnon Dnon]

some images 64x64 size on disk 8.00 KB (8,192 bytes) and others are 12.0 KB (12,288 bytes)

[Jan]

The question is not clear. Which network has which problem? In which format are the images saved? If you store a 64*64 matrix as UINT16 in binary format, the resulting file has 8192 bytes. If you store an image with 64*64 pixels as RGB with UINT8 data, it has 12288 bytes. But your observation can have other reasons also. So it is your turn to explain, how you create the different files and which problems you actually have.