I'm sorry I missed seeing your previous couple of posts; I probably could have saved you some time and frustration.
First a word about the automatic sizing of pictures in tables: When you set a table's AutoFit to "Fixed Column Width", and then you paste a picture into one of its cells (assuming the picture's original width is larger than the cell's width), Word will shrink the picture to the width of the cell (minus the cell's left and right margins). The resizing will be done while retaining the picture's aspect ratio to prevent distortion, so the cell's height must expand to fit the picture's new height.
You can, if you wish, set a fixed height for one or more rows of the table. You do that by selecting the row(s), right-clicking and choosing Table Properties, and going to the Row tab of the Properties dialog to specify the height and choosing "Exactly" in the right-hand dropdown.

The result of setting an exact row height after a picture was already in place is that the picture will be cut off at the bottom. (The rest of the picture is still there, but it can't be shown.) This is not the same as cropping the picture, which removes the extra part.
The result of setting an exact row height before a picture is inserted is that the picture's height will be sized to fit the row, and its width will be whatever preserves the aspect ratio.

I doubt that any of this is the effect you're looking for, so it's best not to rely on automatic resizing. The proper way to handle your requirements is to edit, crop, and resize each picture in a real graphics program before you insert it into the Word table. There are many such programs, ranging from the Paint program that comes with Windows, to the free program IrfanView (https://www.irfanview.com/ ), to professional-quality paid programs such as PhotoShop or PhotoShop Elements.
For removing the lines (cell borders), Ctrl+Alt+U should work reliably as long as the cursor is inside the table. Another way to do it is to select the whole table, click the bottom part of the Borders button on the Table Design ribbon, and click "No Border".