Hi,
I'm going to make a few guesses here and assume that it's because your file sizes are over the limit set for the forum (which is pretty generous anyway). The thing is that modern cameras and even some phones now will take shots at such a high resolution that the file sizes are just too big to view online, so you have to reduce them.
The first time you try it you will think it's a hassle, but after a couple of tries it will be second nature. If you have photo-editing software on your PC then it's easy because most packages contain an option to "resize" the image. I use Adobe Photoshop which is fairly typical - you either specify a percentage of the original or select the pixel size of the final image. If you use percentage it's a trial and error thing until you get the right file size, if you can do pixels then I normally set mine to either 800x600 or 640x480 which works fine on most forums.
Right - details. The easiest way is if you have editing software, but if not and you're running windows you can just about do it with the Microsoft package. I'm still running XP and to resize an image in that, if you look at the picture in "Windows Picture & Fax Viewer" (just click and it's automatic) then at the bottom right of the icons there's one just before the help icon that says "close image and open for editing".
Do that and it will open up the image in "Microsoft Paint", a fairly crude graphics package but it will work. From the top menu select "Image" and then "Stretch/Skew" from the options. On the top box, "Stretch", it shows the current size as 100%. Enter something like 10 or 15 in both Horizontal & Vertical boxes and the image will shrink. Then on the "File" menu, select "save as". I normally keep a similar file name to the original, for example "P100070.jpg" I'll save as "P100070a.jpg". By doing that process I can easily shrink a 7,000KB image file to 140KB, well under the allowances for most forums.
If you don't have the same system then there are loads of free photo editing packages available for Apple/Windoze/Linux which will do the job and there are even places on-line where you can resize over the internet.
Hope that helps, if not come back and we'll work on it because ....
Brian
edit to add.....
As I said, loads of free software out there to do the job for you. For example something like this should do the job nicely.
http://www.freepicturesolutions.com/free-picture-resizer.html