What [...] is this!?! Okey, SPOILER seems to be necessary here... The shield should be obvious (symmetry). The center is horizontally symmetric along row 14 (e.g. the 3s´ intersection is at r14/c7). It´s not logical even from this point on, but I´m sure you can finish it...
A in-depth hint: - Border is connected, horizontally and vertically symmetrical - the image inside is also connected together, but only horizontally symmetrically, though at a different row than the border - r13:c1,c7,c9-10,c14-15,c17-18,c25 - r18:c4,c10,c15-16,c22.
Managed to guess my way through the puzzle. There are multiple solutions. Thank you Joe Tramp & JunkyThrowy for the hints.
An additional hint: From R16, C6 there is a diagonal line extending to R7, C13. Counting rows from the top, the inner image is horizontally symmetrical along R16.
- Border is connected, horizontally and vertically symmetrical
- the image inside is also connected together, but only horizontally symmetrically, though at a different row than the border
- r13:c1,c7,c9-10,c14-15,c17-18,c25
- r18:c4,c10,c15-16,c22.
An additional hint:
From R16, C6 there is a diagonal line extending to R7, C13. Counting rows from the top, the inner image is horizontally symmetrical along R16.
R2 - C12,14
R3 - C11,15
R4 - C6-10, 16-20
R5 - C5,21
R6 - C4,22
R7 - C4,13,22
R8 - C4,12,22
R9 - C4,11,22
R10 - C4,9,22
R11 - C3,9,13-14,17-18,23
R12 - C2,8,11-12,15-16,19-20,24
R13 - C1,7,9-10,14-15,17-18,25
R14 - C2,6-8,19-20,24
And the rest is just a mirror image.